diff --git a/lib/analyze-action-post.js b/lib/analyze-action-post.js
index d40047e2a..d3c48ec15 100644
--- a/lib/analyze-action-post.js
+++ b/lib/analyze-action-post.js
@@ -162634,7 +162634,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/lib/analyze-action.js b/lib/analyze-action.js
index 6d6eae83a..d97180672 100644
--- a/lib/analyze-action.js
+++ b/lib/analyze-action.js
@@ -108708,7 +108708,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
@@ -113381,7 +113381,11 @@ function doesGoExtractionOutputExist(config) {
     config,
     "go" /* go */
   );
-  const trapDirectory = import_path4.default.join(golangDbDirectory, "trap", "go" /* go */);
+  const trapDirectory = import_path4.default.join(
+    golangDbDirectory,
+    "trap",
+    "go" /* go */
+  );
   return fs18.existsSync(trapDirectory) && fs18.readdirSync(trapDirectory).some(
     (fileName) => [
       ".trap",
diff --git a/lib/autobuild-action.js b/lib/autobuild-action.js
index 3c72ad257..12ffc8698 100644
--- a/lib/autobuild-action.js
+++ b/lib/autobuild-action.js
@@ -105009,7 +105009,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/lib/init-action-post.js b/lib/init-action-post.js
index 33eef9731..5f640a889 100644
--- a/lib/init-action-post.js
+++ b/lib/init-action-post.js
@@ -166494,7 +166494,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var fs7 = __toESM(require("fs"));
diff --git a/lib/init-action.js b/lib/init-action.js
index 6f5a5ad32..864d44637 100644
--- a/lib/init-action.js
+++ b/lib/init-action.js
@@ -106401,20 +106401,20 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var KnownLanguage = /* @__PURE__ */ ((KnownLanguage2) => {
-  KnownLanguage2["actions"] = "actions";
-  KnownLanguage2["cpp"] = "cpp";
-  KnownLanguage2["csharp"] = "csharp";
-  KnownLanguage2["go"] = "go";
-  KnownLanguage2["java"] = "java";
-  KnownLanguage2["javascript"] = "javascript";
-  KnownLanguage2["python"] = "python";
-  KnownLanguage2["ruby"] = "ruby";
-  KnownLanguage2["rust"] = "rust";
-  KnownLanguage2["swift"] = "swift";
-  return KnownLanguage2;
-})(KnownLanguage || {});
-var knownLanguageSet = new Set(builtin_default.languages);
+var BuiltInLanguage = /* @__PURE__ */ ((BuiltInLanguage2) => {
+  BuiltInLanguage2["actions"] = "actions";
+  BuiltInLanguage2["cpp"] = "cpp";
+  BuiltInLanguage2["csharp"] = "csharp";
+  BuiltInLanguage2["go"] = "go";
+  BuiltInLanguage2["java"] = "java";
+  BuiltInLanguage2["javascript"] = "javascript";
+  BuiltInLanguage2["python"] = "python";
+  BuiltInLanguage2["ruby"] = "ruby";
+  BuiltInLanguage2["rust"] = "rust";
+  BuiltInLanguage2["swift"] = "swift";
+  return BuiltInLanguage2;
+})(BuiltInLanguage || {});
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/diagnostics.ts
 async function addOverlayDisablementDiagnostics(config, codeql, overlayDisabledReason) {
@@ -106677,7 +106677,7 @@ async function getSupportedLanguageMap(codeql, logger) {
   }
   const supportedLanguages = {};
   for (const extractor of Object.keys(resolveResult.extractors)) {
-    if (resolveSupportedLanguagesUsingCli || KnownLanguage[extractor] !== void 0) {
+    if (resolveSupportedLanguagesUsingCli || BuiltInLanguage[extractor] !== void 0) {
       supportedLanguages[extractor] = extractor;
     }
   }
diff --git a/lib/resolve-environment-action.js b/lib/resolve-environment-action.js
index fd441b9d1..bb743ecee 100644
--- a/lib/resolve-environment-action.js
+++ b/lib/resolve-environment-action.js
@@ -104677,7 +104677,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/lib/setup-codeql-action.js b/lib/setup-codeql-action.js
index e6fe90383..427a5be32 100644
--- a/lib/setup-codeql-action.js
+++ b/lib/setup-codeql-action.js
@@ -105242,7 +105242,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/lib/start-proxy-action-post.js b/lib/start-proxy-action-post.js
index bbe938bed..da5e1afcf 100644
--- a/lib/start-proxy-action-post.js
+++ b/lib/start-proxy-action-post.js
@@ -161961,7 +161961,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/lib/start-proxy-action.js b/lib/start-proxy-action.js
index 0662f93bf..d2fb71a72 100644
--- a/lib/start-proxy-action.js
+++ b/lib/start-proxy-action.js
@@ -121660,14 +121660,14 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
-function isKnownLanguage(language) {
-  return knownLanguageSet.has(language);
+var builtInLanguageSet = new Set(builtin_default.languages);
+function isBuiltInLanguage(language) {
+  return builtInLanguageSet.has(language);
 }
 function parseBuiltInLanguage(language) {
   language = language.trim().toLowerCase();
   language = builtin_default.aliases[language] ?? language;
-  if (isKnownLanguage(language)) {
+  if (isBuiltInLanguage(language)) {
     return language;
   }
   return void 0;
diff --git a/lib/upload-lib.js b/lib/upload-lib.js
index b89bf7dd7..94232f50d 100644
--- a/lib/upload-lib.js
+++ b/lib/upload-lib.js
@@ -107856,7 +107856,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/lib/upload-sarif-action-post.js b/lib/upload-sarif-action-post.js
index f439250c3..33e1d91fb 100644
--- a/lib/upload-sarif-action-post.js
+++ b/lib/upload-sarif-action-post.js
@@ -162131,7 +162131,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache6());
diff --git a/lib/upload-sarif-action.js b/lib/upload-sarif-action.js
index 6d92c1fb9..f754942ec 100644
--- a/lib/upload-sarif-action.js
+++ b/lib/upload-sarif-action.js
@@ -108048,7 +108048,7 @@ var builtin_default = {
 };
 
 // src/languages/index.ts
-var knownLanguageSet = new Set(builtin_default.languages);
+var builtInLanguageSet = new Set(builtin_default.languages);
 
 // src/overlay/status.ts
 var actionsCache2 = __toESM(require_cache5());
diff --git a/pr-checks/sync.ts b/pr-checks/sync.ts
index 8a1842323..e46fca248 100755
--- a/pr-checks/sync.ts
+++ b/pr-checks/sync.ts
@@ -5,7 +5,7 @@ import * as path from "path";
 
 import * as yaml from "yaml";
 
-import { KnownLanguage } from "../src/languages";
+import { BuiltInLanguage } from "../src/languages";
 
 /** Known workflow input names. */
 enum KnownInputName {
@@ -91,8 +91,8 @@ interface LanguageSetup {
   steps: Step[];
 }
 
-/** Describes partial mappings from known languages to their specific setup information. */
-type LanguageSetups = Partial<Record<KnownLanguage, LanguageSetup>>;
+/** Describes partial mappings from built-in languages to their specific setup information. */
+type LanguageSetups = Partial<Record<BuiltInLanguage, LanguageSetup>>;
 
 // The default set of CodeQL Bundle versions to use for the PR checks.
 const defaultTestVersions = [
@@ -125,7 +125,7 @@ const defaultLanguageVersions = {
   java: "17",
   python: "3.13",
   csharp: "9.x",
-} as const satisfies Partial<Record<KnownLanguage, string>>;
+} as const satisfies Partial<Record<BuiltInLanguage, string>>;
 
 /** A mapping from known input names to their specifications. */
 const inputSpecs: WorkflowInputs = {
@@ -364,7 +364,7 @@ function getSetupSteps(checkSpecification: JobSpecification): {
   const inputs: Array<Set<KnownInputName>> = [];
   const steps: Step[] = [];
 
-  for (const language of Object.values(KnownLanguage).sort()) {
+  for (const language of Object.values(BuiltInLanguage).sort()) {
     const setupSpec = languageSetups[language];
 
     if (
diff --git a/src/analyze-action.ts b/src/analyze-action.ts
index 24f8fe612..f67fe699e 100644
--- a/src/analyze-action.ts
+++ b/src/analyze-action.ts
@@ -30,7 +30,7 @@ import {
 } from "./dependency-caching";
 import { EnvVar } from "./environment";
 import { initFeatures } from "./feature-flags";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { getActionsLogger, Logger } from "./logging";
 import { cleanupAndUploadOverlayBaseDatabaseToCache } from "./overlay";
 import { getRepositoryNwo } from "./repository";
@@ -135,9 +135,13 @@ function hasBadExpectErrorInput(): boolean {
 function doesGoExtractionOutputExist(config: Config): boolean {
   const golangDbDirectory = util.getCodeQLDatabasePath(
     config,
-    KnownLanguage.go,
+    BuiltInLanguage.go,
+  );
+  const trapDirectory = path.join(
+    golangDbDirectory,
+    "trap",
+    BuiltInLanguage.go,
   );
-  const trapDirectory = path.join(golangDbDirectory, "trap", KnownLanguage.go);
   return (
     fs.existsSync(trapDirectory) &&
     fs
@@ -169,7 +173,7 @@ function doesGoExtractionOutputExist(config: Config): boolean {
  * whether any extraction output already exists for Go.
  */
 async function runAutobuildIfLegacyGoWorkflow(config: Config, logger: Logger) {
-  if (!config.languages.includes(KnownLanguage.go)) {
+  if (!config.languages.includes(BuiltInLanguage.go)) {
     return;
   }
   if (config.buildMode) {
@@ -182,7 +186,7 @@ async function runAutobuildIfLegacyGoWorkflow(config: Config, logger: Logger) {
     logger.debug("Won't run Go autobuild since it has already been run.");
     return;
   }
-  if (dbIsFinalized(config, KnownLanguage.go, logger)) {
+  if (dbIsFinalized(config, BuiltInLanguage.go, logger)) {
     logger.debug(
       "Won't run Go autobuild since there is already a finalized database for Go.",
     );
@@ -205,7 +209,7 @@ async function runAutobuildIfLegacyGoWorkflow(config: Config, logger: Logger) {
   logger.debug(
     "Running Go autobuild because extraction output (TRAP files) for Go code has not been found.",
   );
-  await runAutobuild(config, KnownLanguage.go, logger);
+  await runAutobuild(config, BuiltInLanguage.go, logger);
 }
 
 async function run(startedAt: Date) {
diff --git a/src/analyze.test.ts b/src/analyze.test.ts
index 0749a0cc2..7523d239b 100644
--- a/src/analyze.test.ts
+++ b/src/analyze.test.ts
@@ -14,7 +14,7 @@ import {
 } from "./analyze";
 import { createStubCodeQL } from "./codeql";
 import { Feature } from "./feature-flags";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { getRunnerLogger } from "./logging";
 import {
   setupTests,
@@ -41,7 +41,7 @@ test.serial("status report fields", async (t) => {
     const threadsFlag = "";
     sinon.stub(uploadLib, "validateSarifFileSchema");
 
-    for (const language of Object.values(KnownLanguage)) {
+    for (const language of Object.values(BuiltInLanguage)) {
       const codeql = createStubCodeQL({
         databaseRunQueries: async () => {},
         databaseInterpretResults: async (
@@ -130,13 +130,13 @@ test.serial("status report fields", async (t) => {
 test("resolveQuerySuiteAlias", (t) => {
   // default query suite names should resolve to something language-specific ending in `.qls`.
   for (const suite of defaultSuites) {
-    const resolved = resolveQuerySuiteAlias(KnownLanguage.go, suite);
+    const resolved = resolveQuerySuiteAlias(BuiltInLanguage.go, suite);
     t.assert(
       path.extname(resolved) === ".qls",
       "Resolved default suite doesn't end in .qls",
     );
     t.assert(
-      resolved.indexOf(KnownLanguage.go) >= 0,
+      resolved.indexOf(BuiltInLanguage.go) >= 0,
       "Resolved default suite doesn't contain language name",
     );
   }
@@ -145,12 +145,12 @@ test("resolveQuerySuiteAlias", (t) => {
   const names = ["foo", "bar", "codeql/go-queries@1.0"];
 
   for (const name of names) {
-    t.deepEqual(resolveQuerySuiteAlias(KnownLanguage.go, name), name);
+    t.deepEqual(resolveQuerySuiteAlias(BuiltInLanguage.go, name), name);
   }
 });
 
 test("addSarifExtension", (t) => {
-  for (const language of Object.values(KnownLanguage)) {
+  for (const language of Object.values(BuiltInLanguage)) {
     t.deepEqual(addSarifExtension(CodeScanning, language), `${language}.sarif`);
     t.deepEqual(
       addSarifExtension(CodeQuality, language),
diff --git a/src/analyze.ts b/src/analyze.ts
index d2088c3a3..884dcccea 100644
--- a/src/analyze.ts
+++ b/src/analyze.ts
@@ -21,7 +21,7 @@ import {
 } from "./diff-informed-analysis-utils";
 import { EnvVar } from "./environment";
 import { FeatureEnablement, Feature } from "./feature-flags";
-import { KnownLanguage, Language } from "./languages";
+import { BuiltInLanguage, Language } from "./languages";
 import { Logger, withGroupAsync } from "./logging";
 import { OverlayDatabaseMode } from "./overlay";
 import type * as sarif from "./sarif";
@@ -41,7 +41,7 @@ export class CodeQLAnalysisError extends Error {
   }
 }
 
-type KnownLanguageKey = keyof typeof KnownLanguage;
+type BuiltInLanguageKey = keyof typeof BuiltInLanguage;
 
 type RunQueriesDurationStatusReport = {
   /**
@@ -50,12 +50,12 @@ type RunQueriesDurationStatusReport = {
    * The "builtin" designation is now outdated with the move to CLI config parsing: this is the time
    * taken to run _all_ the queries.
    */
-  [L in KnownLanguageKey as `analyze_builtin_queries_${L}_duration_ms`]?: number;
+  [L in BuiltInLanguageKey as `analyze_builtin_queries_${L}_duration_ms`]?: number;
 };
 
 type InterpretResultsDurationStatusReport = {
   /** Time taken in ms to interpret results for the language (or undefined if this language was not analyzed). */
-  [L in KnownLanguageKey as `interpret_results_${L}_duration_ms`]?: number;
+  [L in BuiltInLanguageKey as `interpret_results_${L}_duration_ms`]?: number;
 };
 
 export interface QueriesStatusReport
@@ -115,12 +115,12 @@ export async function runExtraction(
 
     if (await shouldExtractLanguage(codeql, config, language)) {
       logger.startGroup(`Extracting ${language}`);
-      if (language === KnownLanguage.python) {
+      if (language === BuiltInLanguage.python) {
         await setupPythonExtractor(logger);
       }
       if (config.buildMode) {
         if (
-          language === KnownLanguage.cpp &&
+          language === BuiltInLanguage.cpp &&
           config.buildMode === BuildMode.Autobuild
         ) {
           await setupCppAutobuild(codeql, logger);
@@ -131,14 +131,14 @@ export async function runExtraction(
         // a stable path that caches can be restored into and that we can cache at the
         // end of the workflow (i.e. that does not get removed when the scratch directory is).
         if (
-          language === KnownLanguage.java &&
+          language === BuiltInLanguage.java &&
           config.buildMode === BuildMode.None
         ) {
           process.env["CODEQL_EXTRACTOR_JAVA_OPTION_BUILDLESS_DEPENDENCY_DIR"] =
             getJavaTempDependencyDir();
         }
         if (
-          language === KnownLanguage.csharp &&
+          language === BuiltInLanguage.csharp &&
           config.buildMode === BuildMode.None &&
           (await features.getValue(Feature.CsharpCacheBuildModeNone))
         ) {
@@ -698,7 +698,7 @@ export async function warnIfGoInstalledAfterInit(
 
       addDiagnostic(
         config,
-        KnownLanguage.go,
+        BuiltInLanguage.go,
         makeDiagnostic(
           "go/workflow/go-installed-after-codeql-init",
           "Go was installed after the `codeql-action/init` Action was run",
diff --git a/src/autobuild.ts b/src/autobuild.ts
index 46935bba6..fc4983f4e 100644
--- a/src/autobuild.ts
+++ b/src/autobuild.ts
@@ -7,7 +7,7 @@ import * as configUtils from "./config-utils";
 import { DocUrl } from "./doc-url";
 import { EnvVar } from "./environment";
 import { Feature, featureConfig, initFeatures } from "./feature-flags";
-import { KnownLanguage, Language } from "./languages";
+import { BuiltInLanguage, Language } from "./languages";
 import { Logger } from "./logging";
 import { getRepositoryNwo } from "./repository";
 import { asyncFilter, BuildMode } from "./util";
@@ -72,7 +72,7 @@ export async function determineAutobuildLanguages(
    * version of the CodeQL Action.
    */
   const autobuildLanguagesWithoutGo = autobuildLanguages.filter(
-    (l) => l !== KnownLanguage.go,
+    (l) => l !== BuiltInLanguage.go,
   );
 
   const languages: Language[] = [];
@@ -84,7 +84,7 @@ export async function determineAutobuildLanguages(
   // If Go is requested, run the Go autobuilder last to ensure it doesn't
   // interfere with the other autobuilder.
   if (autobuildLanguages.length !== autobuildLanguagesWithoutGo.length) {
-    languages.push(KnownLanguage.go);
+    languages.push(BuiltInLanguage.go);
   }
 
   logger.debug(`Will autobuild ${languages.join(" and ")}.`);
@@ -156,7 +156,7 @@ export async function runAutobuild(
 ) {
   logger.startGroup(`Attempting to automatically build ${language} code`);
   const codeQL = await getCodeQL(config.codeQLCmd);
-  if (language === KnownLanguage.cpp) {
+  if (language === BuiltInLanguage.cpp) {
     await setupCppAutobuild(codeQL, logger);
   }
   if (config.buildMode) {
@@ -164,7 +164,7 @@ export async function runAutobuild(
   } else {
     await codeQL.runAutobuild(config, language);
   }
-  if (language === KnownLanguage.go) {
+  if (language === BuiltInLanguage.go) {
     core.exportVariable(EnvVar.DID_AUTOBUILD_GOLANG, "true");
   }
   logger.endGroup();
diff --git a/src/codeql.test.ts b/src/codeql.test.ts
index cfbddf4f7..eccad6895 100644
--- a/src/codeql.test.ts
+++ b/src/codeql.test.ts
@@ -21,7 +21,7 @@ import {
 import type { Config } from "./config-utils";
 import * as defaults from "./defaults.json";
 import { DocUrl } from "./doc-url";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { getRunnerLogger } from "./logging";
 import { ToolsSource } from "./setup-codeql";
 import {
@@ -46,7 +46,7 @@ test.beforeEach(() => {
   initializeEnvironment("1.2.3");
 
   stubConfig = createTestConfig({
-    languages: [KnownLanguage.cpp],
+    languages: [BuiltInLanguage.cpp],
   });
 });
 
@@ -115,7 +115,7 @@ async function stubCodeql(): Promise<codeql.CodeQL> {
   sinon.stub(codeqlObject, "getVersion").resolves(makeVersionInfo("2.17.6"));
   sinon
     .stub(codeqlObject, "isTracedLanguage")
-    .withArgs(KnownLanguage.cpp)
+    .withArgs(BuiltInLanguage.cpp)
     .resolves(true);
   return codeqlObject;
 }
@@ -956,7 +956,8 @@ test.serial("runTool summarizes autobuilder errors", async (t) => {
   sinon.stub(io, "which").resolves("");
 
   await t.throwsAsync(
-    async () => await codeqlObject.runAutobuild(stubConfig, KnownLanguage.java),
+    async () =>
+      await codeqlObject.runAutobuild(stubConfig, BuiltInLanguage.java),
     {
       instanceOf: util.ConfigurationError,
       message:
@@ -982,7 +983,8 @@ test.serial("runTool truncates long autobuilder errors", async (t) => {
   sinon.stub(io, "which").resolves("");
 
   await t.throwsAsync(
-    async () => await codeqlObject.runAutobuild(stubConfig, KnownLanguage.java),
+    async () =>
+      await codeqlObject.runAutobuild(stubConfig, BuiltInLanguage.java),
     {
       instanceOf: util.ConfigurationError,
       message:
diff --git a/src/config-utils.test.ts b/src/config-utils.test.ts
index a69836293..6b24bbe3a 100644
--- a/src/config-utils.test.ts
+++ b/src/config-utils.test.ts
@@ -18,7 +18,7 @@ import { Feature } from "./feature-flags";
 import { RepositoryProperties } from "./feature-flags/properties";
 import * as gitUtils from "./git-utils";
 import { GitVersionInfo } from "./git-utils";
-import { KnownLanguage, Language } from "./languages";
+import { BuiltInLanguage, Language } from "./languages";
 import { getRunnerLogger } from "./logging";
 import { CODEQL_OVERLAY_MINIMUM_VERSION, OverlayDatabaseMode } from "./overlay";
 import { OverlayDisabledReason } from "./overlay/diagnostics";
@@ -214,7 +214,7 @@ test.serial("load code quality config", async (t) => {
     // And the config we expect it to result in
     const expectedConfig = createTestConfig({
       analysisKinds: [AnalysisKind.CodeQuality],
-      languages: [KnownLanguage.actions],
+      languages: [BuiltInLanguage.actions],
       // This gets set because we only have `AnalysisKind.CodeQuality`
       computedConfig: {
         "disable-default-queries": true,
@@ -267,7 +267,7 @@ test.serial(
 
       const expectedConfig = createTestConfig({
         analysisKinds: [AnalysisKind.CodeQuality],
-        languages: [KnownLanguage.javascript],
+        languages: [BuiltInLanguage.javascript],
         codeQLCmd: codeql.getPath(),
         computedConfig,
         dbLocation: path.resolve(tempDir, "codeql_databases"),
@@ -517,7 +517,7 @@ test.serial("load non-empty input", async (t) => {
 
     // And the config we expect it to parse to
     const expectedConfig = createTestConfig({
-      languages: [KnownLanguage.javascript],
+      languages: [BuiltInLanguage.javascript],
       buildMode: BuildMode.None,
       originalUserInput: userConfig,
       computedConfig: userConfig,
@@ -891,10 +891,10 @@ const mockRepositoryNwo = parseRepositoryNwo("owner/repo");
       betterResolveLanguages: (options) =>
         Promise.resolve({
           aliases: {
-            "c#": KnownLanguage.csharp,
-            c: KnownLanguage.cpp,
-            kotlin: KnownLanguage.java,
-            typescript: KnownLanguage.javascript,
+            "c#": BuiltInLanguage.csharp,
+            c: BuiltInLanguage.cpp,
+            kotlin: BuiltInLanguage.java,
+            typescript: BuiltInLanguage.javascript,
           },
           extractors: {
             cpp: [stubExtractorEntry],
@@ -943,12 +943,12 @@ const mockRepositoryNwo = parseRepositoryNwo("owner/repo");
 for (const { displayName, language, feature } of [
   {
     displayName: "Java",
-    language: KnownLanguage.java,
+    language: BuiltInLanguage.java,
     feature: Feature.DisableJavaBuildlessEnabled,
   },
   {
     displayName: "C#",
-    language: KnownLanguage.csharp,
+    language: BuiltInLanguage.csharp,
     feature: Feature.DisableCsharpBuildless,
   },
 ]) {
@@ -968,7 +968,7 @@ for (const { displayName, language, feature } of [
     const messages: LoggedMessage[] = [];
     const buildMode = await configUtils.parseBuildModeInput(
       "none",
-      [KnownLanguage.python],
+      [BuiltInLanguage.python],
       createFeatures([feature]),
       getRecordingLogger(messages),
     );
@@ -1018,7 +1018,7 @@ const defaultOverlayDatabaseModeTestSetup: OverlayDatabaseModeTestSetup = {
   isPullRequest: false,
   isDefaultBranch: false,
   buildMode: BuildMode.None,
-  languages: [KnownLanguage.javascript],
+  languages: [BuiltInLanguage.javascript],
   codeqlVersion: CODEQL_OVERLAY_MINIMUM_VERSION,
   gitRoot: "/some/git/root",
   gitVersion: new GitVersionInfo("2.39.0", "2.39.0"),
@@ -1090,7 +1090,7 @@ const checkOverlayEnablementMacro = test.macro({
         sinon
           .stub(codeql, "isTracedLanguage")
           .callsFake(async (lang: Language) => {
-            return lang === KnownLanguage.java;
+            return lang === BuiltInLanguage.java;
           });
 
         // Mock git root detection
@@ -1183,7 +1183,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Ignore feature flag when analyzing non-default branch",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
   },
   {
@@ -1195,7 +1195,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch when feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     isDefaultBranch: true,
   },
@@ -1209,7 +1209,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch when feature enabled with custom analysis",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     codeScanningConfig: {
       packs: ["some-custom-pack@1.0.0"],
@@ -1226,7 +1226,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch when code-scanning feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1243,7 +1243,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch if runner disk space is too low",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1263,7 +1263,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch if we can't determine runner disk space",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1280,7 +1280,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch if runner disk space is too low and skip resource checks flag is enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1302,7 +1302,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch if runner disk space is below v2 limit and v2 resource checks enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1323,7 +1323,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch if runner disk space is between v2 and v1 limits and v2 resource checks enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1345,7 +1345,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch if runner disk space is between v2 and v1 limits and v2 resource checks not enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1365,7 +1365,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch if memory flag is too low",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1382,7 +1382,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch if memory flag is too low but CodeQL >= 2.24.3",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1401,7 +1401,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay-base database on default branch if memory flag is too low and skip resource checks flag is enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1420,7 +1420,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when cached status indicates previous failure",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisJavascript,
@@ -1438,7 +1438,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when cached status indicates previous failure",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisJavascript,
@@ -1456,7 +1456,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when code-scanning feature enabled with disable-default-queries",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1475,7 +1475,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when code-scanning feature enabled with packs",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1494,7 +1494,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when code-scanning feature enabled with queries",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1513,7 +1513,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when code-scanning feature enabled with query-filters",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1532,7 +1532,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when only language-specific feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysisJavascript],
     isDefaultBranch: true,
   },
@@ -1545,7 +1545,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when only code-scanning feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysisCodeScanningJavascript],
     isDefaultBranch: true,
   },
@@ -1558,7 +1558,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay-base database on default branch when language-specific feature disabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis],
     isDefaultBranch: true,
   },
@@ -1571,7 +1571,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay analysis on PR when feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     isPullRequest: true,
   },
@@ -1585,7 +1585,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay analysis on PR when feature enabled with custom analysis",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     codeScanningConfig: {
       packs: ["some-custom-pack@1.0.0"],
@@ -1602,7 +1602,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay analysis on PR when code-scanning feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1619,7 +1619,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR if runner disk space is too low",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1639,7 +1639,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay analysis on PR if runner disk space is too low and skip resource checks flag is enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1661,7 +1661,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR if we can't determine runner disk space",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1678,7 +1678,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR if memory flag is too low",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1695,7 +1695,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay analysis on PR if memory flag is too low but CodeQL >= 2.24.3",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1714,7 +1714,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay analysis on PR if memory flag is too low and skip resource checks flag is enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1733,7 +1733,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when code-scanning feature enabled with disable-default-queries",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1752,7 +1752,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when code-scanning feature enabled with packs",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1771,7 +1771,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when code-scanning feature enabled with queries",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1790,7 +1790,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when code-scanning feature enabled with query-filters",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [
       Feature.OverlayAnalysis,
       Feature.OverlayAnalysisCodeScanningJavascript,
@@ -1809,7 +1809,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when only language-specific feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysisJavascript],
     isPullRequest: true,
   },
@@ -1822,7 +1822,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when only code-scanning feature enabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysisCodeScanningJavascript],
     isPullRequest: true,
   },
@@ -1835,7 +1835,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis on PR when language-specific feature disabled",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis],
     isPullRequest: true,
   },
@@ -1873,7 +1873,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay PR analysis by feature flag",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     isPullRequest: true,
   },
@@ -1889,7 +1889,7 @@ test.serial(
   {
     overlayDatabaseEnvVar: "overlay",
     buildMode: BuildMode.Autobuild,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
   },
   {
     disabledReason: OverlayDisabledReason.IncompatibleBuildMode,
@@ -1902,7 +1902,7 @@ test.serial(
   {
     overlayDatabaseEnvVar: "overlay",
     buildMode: undefined,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
   },
   {
     disabledReason: OverlayDisabledReason.IncompatibleBuildMode,
@@ -1977,7 +1977,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay when disabled via repository property",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     isPullRequest: true,
     repositoryProperties: {
@@ -1993,7 +1993,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "Overlay not disabled when repository property is false",
   {
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     features: [Feature.OverlayAnalysis, Feature.OverlayAnalysisJavascript],
     isPullRequest: true,
     repositoryProperties: {
@@ -2022,7 +2022,7 @@ test.serial(
 );
 
 // Exercise language-specific overlay analysis features code paths
-for (const language in KnownLanguage) {
+for (const language in BuiltInLanguage) {
   test.serial(
     checkOverlayEnablementMacro,
     `Check default overlay analysis feature for ${language}`,
@@ -2045,7 +2045,7 @@ test.serial(
   checkOverlayEnablementMacro,
   "No overlay analysis for language without per-language overlay feature flag",
   {
-    languages: [KnownLanguage.swift],
+    languages: [BuiltInLanguage.swift],
     features: [Feature.OverlayAnalysis],
     isPullRequest: true,
   },
diff --git a/src/config-utils.ts b/src/config-utils.ts
index 55d5afa72..1147a1ecd 100644
--- a/src/config-utils.ts
+++ b/src/config-utils.ts
@@ -48,7 +48,7 @@ import {
   hasSubmodules,
   isAnalyzingDefaultBranch,
 } from "./git-utils";
-import { KnownLanguage, Language } from "./languages";
+import { BuiltInLanguage, Language } from "./languages";
 import { Logger } from "./logging";
 import { CODEQL_OVERLAY_MINIMUM_VERSION, OverlayDatabaseMode } from "./overlay";
 import {
@@ -273,10 +273,10 @@ async function getSupportedLanguageMap(
   for (const extractor of Object.keys(resolveResult.extractors)) {
     // If the CLI supports resolving languages with default queries, use these
     // as the set of supported languages. Otherwise, require the language to be
-    // a known language.
+    // a built-in language.
     if (
       resolveSupportedLanguagesUsingCli ||
-      KnownLanguage[extractor] !== undefined
+      BuiltInLanguage[extractor] !== undefined
     ) {
       supportedLanguages[extractor] = extractor;
     }
@@ -946,7 +946,7 @@ async function validateOverlayDatabaseMode(
       await Promise.all(
         languages.map(
           async (l) =>
-            l !== KnownLanguage.go && // Workaround to allow overlay analysis for Go with any build
+            l !== BuiltInLanguage.go && // Workaround to allow overlay analysis for Go with any build
             // mode, since it does not yet support BMN. The Go autobuilder and/or extractor will
             // ensure that overlay-base databases are only created for supported Go build setups,
             // and that we'll fall back to full databases in other cases.
@@ -1035,13 +1035,13 @@ async function setCppTrapCachingEnvironmentVariables(
   config: Config,
   logger: Logger,
 ): Promise<void> {
-  if (config.languages.includes(KnownLanguage.cpp)) {
+  if (config.languages.includes(BuiltInLanguage.cpp)) {
     const envVar = "CODEQL_EXTRACTOR_CPP_TRAP_CACHING";
     if (process.env[envVar]) {
       logger.info(
         `Environment variable ${envVar} already set, leaving it unchanged.`,
       );
-    } else if (config.trapCaches[KnownLanguage.cpp]) {
+    } else if (config.trapCaches[BuiltInLanguage.cpp]) {
       logger.info("Enabling TRAP caching for C/C++.");
       core.exportVariable(envVar, "true");
     } else {
@@ -1538,7 +1538,7 @@ export async function parseBuildModeInput(
   }
 
   if (
-    languages.includes(KnownLanguage.csharp) &&
+    languages.includes(BuiltInLanguage.csharp) &&
     (await features.getValue(Feature.DisableCsharpBuildless))
   ) {
     logger.warning(
@@ -1548,7 +1548,7 @@ export async function parseBuildModeInput(
   }
 
   if (
-    languages.includes(KnownLanguage.java) &&
+    languages.includes(BuiltInLanguage.java) &&
     (await features.getValue(Feature.DisableJavaBuildlessEnabled))
   ) {
     logger.warning(
diff --git a/src/config/db-config.test.ts b/src/config/db-config.test.ts
index d7ff48eed..d0c11d268 100644
--- a/src/config/db-config.test.ts
+++ b/src/config/db-config.test.ts
@@ -1,7 +1,7 @@
 import test, { ExecutionContext } from "ava";
 
 import { RepositoryProperties } from "../feature-flags/properties";
-import { KnownLanguage, Language } from "../languages";
+import { BuiltInLanguage, Language } from "../languages";
 import { getRunnerLogger } from "../logging";
 import {
   checkExpectedLogMessages,
@@ -54,7 +54,7 @@ const invalidPackNameMacro = test.macro({
     parsePacksErrorMacro.exec(
       t,
       name,
-      [KnownLanguage.cpp],
+      [BuiltInLanguage.cpp],
       new RegExp(`^"${name}" is not a valid pack$`),
     ),
   title: (_providedTitle: string | undefined, arg: string | undefined) =>
@@ -62,23 +62,23 @@ const invalidPackNameMacro = test.macro({
 });
 
 test("no packs", parsePacksMacro, "", [], undefined);
-test("two packs", parsePacksMacro, "a/b,c/d@1.2.3", [KnownLanguage.cpp], {
-  [KnownLanguage.cpp]: ["a/b", "c/d@1.2.3"],
+test("two packs", parsePacksMacro, "a/b,c/d@1.2.3", [BuiltInLanguage.cpp], {
+  [BuiltInLanguage.cpp]: ["a/b", "c/d@1.2.3"],
 });
 test(
   "two packs with spaces",
   parsePacksMacro,
   " a/b , c/d@1.2.3 ",
-  [KnownLanguage.cpp],
+  [BuiltInLanguage.cpp],
   {
-    [KnownLanguage.cpp]: ["a/b", "c/d@1.2.3"],
+    [BuiltInLanguage.cpp]: ["a/b", "c/d@1.2.3"],
   },
 );
 test(
   "two packs with language",
   parsePacksErrorMacro,
   "a/b,c/d@1.2.3",
-  [KnownLanguage.cpp, KnownLanguage.java],
+  [BuiltInLanguage.cpp, BuiltInLanguage.java],
   new RegExp(
     "Cannot specify a 'packs' input in a multi-language analysis. " +
       "Use a codeql-config.yml file instead and specify packs by language.",
@@ -106,9 +106,9 @@ test(
     // (globbing is not done)
     "c/d@1.2.3:+*)_(",
   ].join(","),
-  [KnownLanguage.cpp],
+  [BuiltInLanguage.cpp],
   {
-    [KnownLanguage.cpp]: [
+    [BuiltInLanguage.cpp]: [
       "c/d@1.0",
       "c/d@~1.0.0",
       "c/d@~1.0.0:a/b",
@@ -215,7 +215,7 @@ test(
   "All empty",
   undefined,
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   {
     ...dbConfig.defaultAugmentationProperties,
@@ -227,7 +227,7 @@ test(
   "With queries",
   undefined,
   " a, b , c, d",
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   {
     ...dbConfig.defaultAugmentationProperties,
@@ -240,7 +240,7 @@ test(
   "With queries combining",
   undefined,
   "   +   a, b , c, d ",
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   {
     ...dbConfig.defaultAugmentationProperties,
@@ -254,7 +254,7 @@ test(
   "With packs",
   "   codeql/a , codeql/b   , codeql/c  , codeql/d  ",
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   {
     ...dbConfig.defaultAugmentationProperties,
@@ -267,7 +267,7 @@ test(
   "With packs combining",
   "   +   codeql/a, codeql/b, codeql/c, codeql/d",
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   {
     ...dbConfig.defaultAugmentationProperties,
@@ -281,7 +281,7 @@ test(
   "With repo property queries",
   undefined,
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {
     "github-codeql-extra-queries": "a, b, c, d",
   },
@@ -299,7 +299,7 @@ test(
   "With repo property queries combining",
   undefined,
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {
     "github-codeql-extra-queries": "+ a, b, c, d",
   },
@@ -341,7 +341,7 @@ test(
   "Plus (+) with nothing else (queries)",
   undefined,
   "   +   ",
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   /The workflow property "queries" is invalid/,
 );
@@ -351,7 +351,7 @@ test(
   "Plus (+) with nothing else (packs)",
   "   +   ",
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   /The workflow property "packs" is invalid/,
 );
@@ -361,7 +361,7 @@ test(
   "Plus (+) with nothing else (repo property queries)",
   undefined,
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {
     "github-codeql-extra-queries": "    + ",
   },
@@ -373,7 +373,7 @@ test(
   "Packs input with multiple languages",
   "   +  a/b, c/d ",
   undefined,
-  [KnownLanguage.javascript, KnownLanguage.java],
+  [BuiltInLanguage.javascript, BuiltInLanguage.java],
   {},
   /Cannot specify a 'packs' input in a multi-language analysis/,
 );
@@ -393,7 +393,7 @@ test(
   "Invalid packs",
   " a-pack-without-a-scope ",
   undefined,
-  [KnownLanguage.javascript],
+  [BuiltInLanguage.javascript],
   {},
   /"a-pack-without-a-scope" is not a valid pack/,
 );
diff --git a/src/database-upload.test.ts b/src/database-upload.test.ts
index c4ac59e76..1cfbaecad 100644
--- a/src/database-upload.test.ts
+++ b/src/database-upload.test.ts
@@ -12,7 +12,7 @@ import { createStubCodeQL } from "./codeql";
 import { Config } from "./config-utils";
 import { cleanupAndUploadDatabases } from "./database-upload";
 import * as gitUtils from "./git-utils";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { RepositoryNwo } from "./repository";
 import {
   checkExpectedLogMessages,
@@ -45,7 +45,7 @@ const testApiDetails: GitHubApiDetails = {
 
 function getTestConfig(tmpDir: string): Config {
   return createTestConfig({
-    languages: [KnownLanguage.javascript],
+    languages: [BuiltInLanguage.javascript],
     dbLocation: tmpDir,
   });
 }
diff --git a/src/dependency-caching.test.ts b/src/dependency-caching.test.ts
index a2d75190d..e611cd03e 100644
--- a/src/dependency-caching.test.ts
+++ b/src/dependency-caching.test.ts
@@ -27,7 +27,7 @@ import {
   CacheStoreResult,
 } from "./dependency-caching";
 import { Feature } from "./feature-flags";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import {
   setupTests,
   createFeatures,
@@ -179,7 +179,7 @@ test("checkHashPatterns - logs when no patterns match", async (t) => {
   const result = await checkHashPatterns(
     codeql,
     features,
-    KnownLanguage.csharp,
+    BuiltInLanguage.csharp,
     config,
     "download",
     getRecordingLogger(messages),
@@ -208,7 +208,7 @@ test("checkHashPatterns - returns patterns when patterns match", async (t) => {
     const result = await checkHashPatterns(
       codeql,
       features,
-      KnownLanguage.csharp,
+      BuiltInLanguage.csharp,
       config,
       "upload",
       getRecordingLogger(messages),
@@ -270,7 +270,7 @@ test.serial(
     const keyWithFeature = await cacheKey(
       codeql,
       createFeatures([Feature.CsharpNewCacheKey]),
-      KnownLanguage.csharp,
+      BuiltInLanguage.csharp,
       // Patterns don't matter here because we have stubbed `hashFiles` to always return a specific hash above.
       [],
     );
@@ -288,12 +288,12 @@ test.serial(
     const result = await downloadDependencyCaches(
       codeql,
       createFeatures([]),
-      [KnownLanguage.csharp],
+      [BuiltInLanguage.csharp],
       logger,
     );
     const statusReport = result.statusReport;
     t.is(statusReport.length, 1);
-    t.is(statusReport[0].language, KnownLanguage.csharp);
+    t.is(statusReport[0].language, BuiltInLanguage.csharp);
     t.is(statusReport[0].hit_kind, CacheHitKind.Miss);
     t.deepEqual(result.restoredKeys, []);
     t.assert(restoreCacheStub.calledOnce);
@@ -316,7 +316,7 @@ test.serial(
     const keyWithFeature = await cacheKey(
       codeql,
       features,
-      KnownLanguage.csharp,
+      BuiltInLanguage.csharp,
       // Patterns don't matter here because we have stubbed `hashFiles` to always return a specific hash above.
       [],
     );
@@ -334,14 +334,14 @@ test.serial(
     const result = await downloadDependencyCaches(
       codeql,
       features,
-      [KnownLanguage.csharp],
+      [BuiltInLanguage.csharp],
       logger,
     );
 
     // Check that the status report for telemetry indicates that one cache was restored with an exact match.
     const statusReport = result.statusReport;
     t.is(statusReport.length, 1);
-    t.is(statusReport[0].language, KnownLanguage.csharp);
+    t.is(statusReport[0].language, BuiltInLanguage.csharp);
     t.is(statusReport[0].hit_kind, CacheHitKind.Exact);
 
     // Check that the restored key has been returned.
@@ -380,7 +380,7 @@ test.serial(
     const keyWithFeature = await cacheKey(
       codeql,
       features,
-      KnownLanguage.csharp,
+      BuiltInLanguage.csharp,
       // Patterns don't matter here because we have stubbed `hashFiles` to always return a specific hash above.
       [],
     );
@@ -398,14 +398,14 @@ test.serial(
     const result = await downloadDependencyCaches(
       codeql,
       features,
-      [KnownLanguage.csharp],
+      [BuiltInLanguage.csharp],
       logger,
     );
 
     // Check that the status report for telemetry indicates that one cache was restored with a partial match.
     const statusReport = result.statusReport;
     t.is(statusReport.length, 1);
-    t.is(statusReport[0].language, KnownLanguage.csharp);
+    t.is(statusReport[0].language, BuiltInLanguage.csharp);
     t.is(statusReport[0].hit_kind, CacheHitKind.Partial);
 
     // Check that the restored key has been returned.
@@ -426,7 +426,7 @@ test("uploadDependencyCaches - skips upload for a language with no cache config"
   const logger = getRecordingLogger(messages);
   const features = createFeatures([]);
   const config = createTestConfig({
-    languages: [KnownLanguage.actions],
+    languages: [BuiltInLanguage.actions],
   });
 
   const result = await uploadDependencyCaches(codeql, features, config, logger);
@@ -444,7 +444,7 @@ test.serial(
     const logger = getRecordingLogger(messages);
     const features = createFeatures([]);
     const config = createTestConfig({
-      languages: [KnownLanguage.go],
+      languages: [BuiltInLanguage.go],
     });
 
     const makePatternCheckStub = sinon.stub(internal, "makePatternCheck");
@@ -457,7 +457,7 @@ test.serial(
       logger,
     );
     t.is(result.length, 1);
-    t.is(result[0].language, KnownLanguage.go);
+    t.is(result[0].language, BuiltInLanguage.go);
     t.is(result[0].result, CacheStoreResult.NoHash);
   },
 );
@@ -483,12 +483,12 @@ test.serial(
     const primaryCacheKey = await cacheKey(
       codeql,
       features,
-      KnownLanguage.csharp,
+      BuiltInLanguage.csharp,
       CSHARP_BASE_PATTERNS,
     );
 
     const config = createTestConfig({
-      languages: [KnownLanguage.csharp],
+      languages: [BuiltInLanguage.csharp],
       dependencyCachingRestoredKeys: [primaryCacheKey],
     });
 
@@ -499,7 +499,7 @@ test.serial(
       logger,
     );
     t.is(result.length, 1);
-    t.is(result[0].language, KnownLanguage.csharp);
+    t.is(result[0].language, BuiltInLanguage.csharp);
     t.is(result[0].result, CacheStoreResult.Duplicate);
   },
 );
@@ -525,7 +525,7 @@ test.serial(
     sinon.stub(cachingUtils, "getTotalCacheSize").resolves(0);
 
     const config = createTestConfig({
-      languages: [KnownLanguage.csharp],
+      languages: [BuiltInLanguage.csharp],
     });
 
     const result = await uploadDependencyCaches(
@@ -535,7 +535,7 @@ test.serial(
       logger,
     );
     t.is(result.length, 1);
-    t.is(result[0].language, KnownLanguage.csharp);
+    t.is(result[0].language, BuiltInLanguage.csharp);
     t.is(result[0].result, CacheStoreResult.Empty);
 
     checkExpectedLogMessages(t, messages, [
@@ -566,7 +566,7 @@ test.serial(
     sinon.stub(actionsCache, "saveCache").resolves();
 
     const config = createTestConfig({
-      languages: [KnownLanguage.csharp],
+      languages: [BuiltInLanguage.csharp],
     });
 
     const result = await uploadDependencyCaches(
@@ -576,7 +576,7 @@ test.serial(
       logger,
     );
     t.is(result.length, 1);
-    t.is(result[0].language, KnownLanguage.csharp);
+    t.is(result[0].language, BuiltInLanguage.csharp);
     t.is(result[0].result, CacheStoreResult.Stored);
     t.is(result[0].upload_size_bytes, 1024);
 
@@ -608,7 +608,7 @@ test.serial(
       .throws(new actionsCache.ReserveCacheError("Already in use"));
 
     const config = createTestConfig({
-      languages: [KnownLanguage.csharp],
+      languages: [BuiltInLanguage.csharp],
     });
 
     await t.notThrowsAsync(async () => {
@@ -619,7 +619,7 @@ test.serial(
         logger,
       );
       t.is(result.length, 1);
-      t.is(result[0].language, KnownLanguage.csharp);
+      t.is(result[0].language, BuiltInLanguage.csharp);
       t.is(result[0].result, CacheStoreResult.Duplicate);
 
       checkExpectedLogMessages(t, messages, ["Not uploading cache for"]);
@@ -647,7 +647,7 @@ test.serial("uploadDependencyCaches - throws other exceptions", async (t) => {
   sinon.stub(actionsCache, "saveCache").throws();
 
   const config = createTestConfig({
-    languages: [KnownLanguage.csharp],
+    languages: [BuiltInLanguage.csharp],
   });
 
   await t.throwsAsync(async () => {
@@ -659,7 +659,7 @@ test("getFeaturePrefix - returns empty string if no features are enabled", async
   const codeql = createStubCodeQL({});
   const features = createFeatures([]);
 
-  for (const knownLanguage of Object.values(KnownLanguage)) {
+  for (const knownLanguage of Object.values(BuiltInLanguage)) {
     const result = await getFeaturePrefix(codeql, features, knownLanguage);
     t.deepEqual(result, "", `Expected no feature prefix for ${knownLanguage}`);
   }
@@ -669,7 +669,11 @@ test("getFeaturePrefix - C# - returns prefix if CsharpNewCacheKey is enabled", a
   const codeql = createStubCodeQL({});
   const features = createFeatures([Feature.CsharpNewCacheKey]);
 
-  const result = await getFeaturePrefix(codeql, features, KnownLanguage.csharp);
+  const result = await getFeaturePrefix(
+    codeql,
+    features,
+    BuiltInLanguage.csharp,
+  );
   t.notDeepEqual(result, "");
   t.assert(result.endsWith("-"));
   // Check the length of the prefix, which should correspond to `cacheKeyHashLength` + 1 for the trailing `-`.
@@ -680,9 +684,9 @@ test("getFeaturePrefix - non-C# - returns '' if CsharpNewCacheKey is enabled", a
   const codeql = createStubCodeQL({});
   const features = createFeatures([Feature.CsharpNewCacheKey]);
 
-  for (const knownLanguage of Object.values(KnownLanguage)) {
+  for (const knownLanguage of Object.values(BuiltInLanguage)) {
     // Skip C# since we expect a result for it, which is tested in the previous test.
-    if (knownLanguage === KnownLanguage.csharp) {
+    if (knownLanguage === BuiltInLanguage.csharp) {
       continue;
     }
     const result = await getFeaturePrefix(codeql, features, knownLanguage);
@@ -694,7 +698,11 @@ test("getFeaturePrefix - C# - returns prefix if CsharpCacheBuildModeNone is enab
   const codeql = createStubCodeQL({});
   const features = createFeatures([Feature.CsharpCacheBuildModeNone]);
 
-  const result = await getFeaturePrefix(codeql, features, KnownLanguage.csharp);
+  const result = await getFeaturePrefix(
+    codeql,
+    features,
+    BuiltInLanguage.csharp,
+  );
   t.notDeepEqual(result, "");
   t.assert(result.endsWith("-"));
   // Check the length of the prefix, which should correspond to `cacheKeyHashLength` + 1 for the trailing `-`.
@@ -705,9 +713,9 @@ test("getFeaturePrefix - non-C# - returns '' if CsharpCacheBuildModeNone is enab
   const codeql = createStubCodeQL({});
   const features = createFeatures([Feature.CsharpCacheBuildModeNone]);
 
-  for (const knownLanguage of Object.values(KnownLanguage)) {
+  for (const knownLanguage of Object.values(BuiltInLanguage)) {
     // Skip C# since we expect a result for it, which is tested in the previous test.
-    if (knownLanguage === KnownLanguage.csharp) {
+    if (knownLanguage === BuiltInLanguage.csharp) {
       continue;
     }
     const result = await getFeaturePrefix(codeql, features, knownLanguage);
diff --git a/src/dependency-caching.ts b/src/dependency-caching.ts
index dc9a140be..f04d38f46 100644
--- a/src/dependency-caching.ts
+++ b/src/dependency-caching.ts
@@ -11,7 +11,7 @@ import { CodeQL } from "./codeql";
 import { Config } from "./config-utils";
 import { EnvVar } from "./environment";
 import { Feature, FeatureEnablement } from "./feature-flags";
-import { KnownLanguage, Language } from "./languages";
+import { BuiltInLanguage, Language } from "./languages";
 import { Logger } from "./logging";
 import { getErrorMessage, getRequiredEnvParam } from "./util";
 
@@ -541,7 +541,7 @@ export async function getFeaturePrefix(
     }
   };
 
-  if (language === KnownLanguage.csharp) {
+  if (language === BuiltInLanguage.csharp) {
     await addFeatureIfEnabled(Feature.CsharpNewCacheKey);
     await addFeatureIfEnabled(Feature.CsharpCacheBuildModeNone);
   }
diff --git a/src/init-action.ts b/src/init-action.ts
index bc95304bf..795378235 100644
--- a/src/init-action.ts
+++ b/src/init-action.ts
@@ -58,7 +58,7 @@ import {
   initConfig,
   runDatabaseInitCluster,
 } from "./init";
-import { JavaEnvVars, KnownLanguage } from "./languages";
+import { JavaEnvVars, BuiltInLanguage } from "./languages";
 import { getActionsLogger, Logger, withGroupAsync } from "./logging";
 import {
   downloadOverlayBaseDatabaseFromCache,
@@ -330,7 +330,7 @@ async function run(startedAt: Date) {
       // requested rust - don't enable it via language autodetection.
       configUtils
         .getRawLanguagesNoAutodetect(getOptionalInput("languages"))
-        .includes(KnownLanguage.rust)
+        .includes(BuiltInLanguage.rust)
     ) {
       const experimental = "2.19.3";
       const publicPreview = "2.22.1";
@@ -390,7 +390,7 @@ async function run(startedAt: Date) {
     });
 
     if (
-      config.languages.includes(KnownLanguage.swift) &&
+      config.languages.includes(BuiltInLanguage.swift) &&
       process.platform !== "darwin"
     ) {
       throw new ConfigurationError(
@@ -509,7 +509,7 @@ async function run(startedAt: Date) {
     }
 
     if (
-      config.languages.includes(KnownLanguage.go) &&
+      config.languages.includes(BuiltInLanguage.go) &&
       process.platform === "linux"
     ) {
       try {
@@ -567,7 +567,7 @@ async function run(startedAt: Date) {
         if (e instanceof FileCmdNotFoundError) {
           addDiagnostic(
             config,
-            KnownLanguage.go,
+            BuiltInLanguage.go,
             makeDiagnostic(
               "go/workflow/file-program-unavailable",
               "The `file` program is required on Linux, but does not appear to be installed",
@@ -661,7 +661,7 @@ async function run(startedAt: Date) {
       (await codeQlVersionAtLeast(codeql, CODEQL_VERSION_JAR_MINIMIZATION)) &&
       config.dependencyCachingEnabled &&
       config.buildMode === BuildMode.None &&
-      config.languages.includes(KnownLanguage.java)
+      config.languages.includes(BuiltInLanguage.java)
     ) {
       core.exportVariable(
         EnvVar.JAVA_EXTRACTOR_MINIMIZE_DEPENDENCY_JARS,
diff --git a/src/init.test.ts b/src/init.test.ts
index 1f1f0de8d..f7add6a9a 100644
--- a/src/init.test.ts
+++ b/src/init.test.ts
@@ -15,7 +15,7 @@ import {
   getFileCoverageInformationEnabled,
   logFileCoverageOnPrsDeprecationWarning,
 } from "./init";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import {
   createFeatures,
   LoggedMessage,
@@ -152,7 +152,7 @@ test("cleanupDatabaseClusterDirectory can disable warning with options", async (
 });
 
 type PackInfo = {
-  language: KnownLanguage;
+  language: BuiltInLanguage;
   packinfoContents: string | undefined;
   sourceOnlyPack?: boolean;
   qlpackFileName?: string;
@@ -169,13 +169,13 @@ const testCheckPacksForOverlayCompatibility = test.macro({
       expectedResult,
     }: {
       cliOverlayVersion: number | undefined;
-      languages: KnownLanguage[];
+      languages: BuiltInLanguage[];
       packs: Record<string, PackInfo>;
       expectedResult: boolean;
     },
   ) => {
     await withTmpDir(async (tmpDir) => {
-      const packDirsByLanguage = new Map<KnownLanguage, string[]>();
+      const packDirsByLanguage = new Map<BuiltInLanguage, string[]>();
 
       for (const [packName, packInfo] of Object.entries(packs)) {
         const packPath = path.join(tmpDir, packName);
@@ -242,10 +242,10 @@ test(
   "returns false when CLI does not support overlay",
   {
     cliOverlayVersion: undefined,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
     },
@@ -258,7 +258,7 @@ test(
   "returns true when there are no query packs",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {},
     expectedResult: true,
   },
@@ -269,10 +269,10 @@ test(
   "returns true when query pack has not been compiled",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: undefined,
         sourceOnlyPack: true,
       },
@@ -286,10 +286,10 @@ test(
   "returns true when query pack has expected overlay version",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
     },
@@ -302,14 +302,14 @@ test(
   "returns true when query packs for all languages to analyze are compatible",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.cpp, KnownLanguage.java],
+    languages: [BuiltInLanguage.cpp, BuiltInLanguage.java],
     packs: {
       "codeql/cpp-queries": {
-        language: KnownLanguage.cpp,
+        language: BuiltInLanguage.cpp,
         packinfoContents: '{"overlayVersion":2}',
       },
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
     },
@@ -322,14 +322,14 @@ test(
   "returns true when query pack for a language not analyzed is incompatible",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/cpp-queries": {
-        language: KnownLanguage.cpp,
+        language: BuiltInLanguage.cpp,
         packinfoContents: undefined,
       },
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
     },
@@ -342,14 +342,14 @@ test(
   "returns false when query pack for a language to analyze is incompatible",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.cpp, KnownLanguage.java],
+    languages: [BuiltInLanguage.cpp, BuiltInLanguage.java],
     packs: {
       "codeql/cpp-queries": {
-        language: KnownLanguage.cpp,
+        language: BuiltInLanguage.cpp,
         packinfoContents: '{"overlayVersion":1}',
       },
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
     },
@@ -362,14 +362,14 @@ test(
   "returns false when query pack is missing .packinfo",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
       "custom/queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: undefined,
       },
     },
@@ -382,14 +382,14 @@ test(
   "returns false when query pack has different overlay version",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
       "custom/queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":1}',
       },
     },
@@ -402,14 +402,14 @@ test(
   "returns false when query pack is missing overlayVersion in .packinfo",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
       "custom/queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: "{}",
       },
     },
@@ -422,14 +422,14 @@ test(
   "returns false when .packinfo is not valid JSON",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
       },
       "custom/queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: "this_is_not_valid_json",
       },
     },
@@ -442,10 +442,10 @@ test(
   "returns true when query pack uses codeql-pack.yml filename",
   {
     cliOverlayVersion: 2,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     packs: {
       "codeql/java-queries": {
-        language: KnownLanguage.java,
+        language: BuiltInLanguage.java,
         packinfoContents: '{"overlayVersion":2}',
         qlpackFileName: "codeql-pack.yml",
       },
diff --git a/src/init.ts b/src/init.ts
index 8e3fa21a4..8ed6f6400 100644
--- a/src/init.ts
+++ b/src/init.ts
@@ -26,7 +26,7 @@ import {
   RepositoryProperties,
   RepositoryPropertyName,
 } from "./feature-flags/properties";
-import { KnownLanguage, Language } from "./languages";
+import { BuiltInLanguage, Language } from "./languages";
 import { Logger, withGroupAsync } from "./logging";
 import { ToolsSource } from "./setup-codeql";
 import { ZstdAvailability } from "./tar";
@@ -235,7 +235,7 @@ export async function checkInstallPython311(
   codeql: CodeQL,
 ) {
   if (
-    languages.includes(KnownLanguage.python) &&
+    languages.includes(BuiltInLanguage.python) &&
     process.platform === "win32" &&
     !(await codeql.getVersion()).features?.supportsPython312
   ) {
diff --git a/src/languages/index.test.ts b/src/languages/index.test.ts
index 048f6b702..4fe1675af 100644
--- a/src/languages/index.test.ts
+++ b/src/languages/index.test.ts
@@ -4,43 +4,43 @@ import { setupTests } from "../testing-utils";
 
 import knownLanguagesData from "./builtin.json";
 
-import { isKnownLanguage, KnownLanguage, parseBuiltInLanguage } from ".";
+import { isBuiltInLanguage, BuiltInLanguage, parseBuiltInLanguage } from ".";
 
 setupTests(test);
 
 test("parseBuiltInLanguage", (t) => {
   // Exact matches
-  t.is(parseBuiltInLanguage("csharp"), KnownLanguage.csharp);
-  t.is(parseBuiltInLanguage("cpp"), KnownLanguage.cpp);
-  t.is(parseBuiltInLanguage("go"), KnownLanguage.go);
-  t.is(parseBuiltInLanguage("java"), KnownLanguage.java);
-  t.is(parseBuiltInLanguage("javascript"), KnownLanguage.javascript);
-  t.is(parseBuiltInLanguage("python"), KnownLanguage.python);
-  t.is(parseBuiltInLanguage("rust"), KnownLanguage.rust);
+  t.is(parseBuiltInLanguage("csharp"), BuiltInLanguage.csharp);
+  t.is(parseBuiltInLanguage("cpp"), BuiltInLanguage.cpp);
+  t.is(parseBuiltInLanguage("go"), BuiltInLanguage.go);
+  t.is(parseBuiltInLanguage("java"), BuiltInLanguage.java);
+  t.is(parseBuiltInLanguage("javascript"), BuiltInLanguage.javascript);
+  t.is(parseBuiltInLanguage("python"), BuiltInLanguage.python);
+  t.is(parseBuiltInLanguage("rust"), BuiltInLanguage.rust);
 
   // Aliases
-  t.is(parseBuiltInLanguage("  \t\nCsHaRp\t\t"), KnownLanguage.csharp);
-  t.is(parseBuiltInLanguage("c"), KnownLanguage.cpp);
-  t.is(parseBuiltInLanguage("c++"), KnownLanguage.cpp);
-  t.is(parseBuiltInLanguage("kotlin"), KnownLanguage.java);
-  t.is(parseBuiltInLanguage("typescript"), KnownLanguage.javascript);
+  t.is(parseBuiltInLanguage("  \t\nCsHaRp\t\t"), BuiltInLanguage.csharp);
+  t.is(parseBuiltInLanguage("c"), BuiltInLanguage.cpp);
+  t.is(parseBuiltInLanguage("c++"), BuiltInLanguage.cpp);
+  t.is(parseBuiltInLanguage("kotlin"), BuiltInLanguage.java);
+  t.is(parseBuiltInLanguage("typescript"), BuiltInLanguage.javascript);
 
   // spaces and case-insensitivity
-  t.is(parseBuiltInLanguage("  \t\nkOtLin\t\t"), KnownLanguage.java);
+  t.is(parseBuiltInLanguage("  \t\nkOtLin\t\t"), BuiltInLanguage.java);
 
   // Not matches
-  t.is(parseBuiltInLanguage(KnownLanguage.python), KnownLanguage.python);
+  t.is(parseBuiltInLanguage(BuiltInLanguage.python), BuiltInLanguage.python);
   t.is(parseBuiltInLanguage("foo"), undefined);
   t.is(parseBuiltInLanguage(" "), undefined);
   t.is(parseBuiltInLanguage(""), undefined);
 });
 
-test("isKnownLanguage matches the curated known-language set", (t) => {
-  t.true(isKnownLanguage(KnownLanguage.actions));
-  t.true(isKnownLanguage(KnownLanguage.swift));
-  t.false(isKnownLanguage("typescript"));
+test("isBuiltInLanguage matches the curated built-in language set", (t) => {
+  t.true(isBuiltInLanguage(BuiltInLanguage.actions));
+  t.true(isBuiltInLanguage(BuiltInLanguage.swift));
+  t.false(isBuiltInLanguage("typescript"));
 });
 
-test("KnownLanguage enum matches builtin.json", (t) => {
-  t.deepEqual(Object.values(KnownLanguage), knownLanguagesData.languages);
+test("BuiltInLanguage enum matches builtin.json", (t) => {
+  t.deepEqual(Object.values(BuiltInLanguage), knownLanguagesData.languages);
 });
diff --git a/src/languages/index.ts b/src/languages/index.ts
index 7187ccc8a..2e91d8f41 100644
--- a/src/languages/index.ts
+++ b/src/languages/index.ts
@@ -3,13 +3,8 @@ import knownLanguagesData from "./builtin.json";
 /** A language to analyze with CodeQL. */
 export type Language = string;
 
-/**
- * A language supported by CodeQL that is treated specially by the Action.
- *
- * This is not an exhaustive list of languages supported by CodeQL and new
- * languages do not need to be added here.
- */
-export enum KnownLanguage {
+/** A language built into the `defaults.json` CodeQL distribution. */
+export enum BuiltInLanguage {
   actions = "actions",
   cpp = "cpp",
   csharp = "csharp",
@@ -30,10 +25,12 @@ export enum JavaEnvVars {
   _JAVA_OPTIONS = "_JAVA_OPTIONS",
 }
 
-const knownLanguageSet = new Set<string>(knownLanguagesData.languages);
+const builtInLanguageSet = new Set<string>(knownLanguagesData.languages);
 
-export function isKnownLanguage(language: string): language is KnownLanguage {
-  return knownLanguageSet.has(language);
+export function isBuiltInLanguage(
+  language: string,
+): language is BuiltInLanguage {
+  return builtInLanguageSet.has(language);
 }
 
 /**
@@ -41,13 +38,13 @@ export function isKnownLanguage(language: string): language is KnownLanguage {
  */
 export function parseBuiltInLanguage(
   language: string,
-): KnownLanguage | undefined {
+): BuiltInLanguage | undefined {
   language = language.trim().toLowerCase();
   language =
     knownLanguagesData.aliases[
       language as keyof typeof knownLanguagesData.aliases
     ] ?? language;
-  if (isKnownLanguage(language)) {
+  if (isBuiltInLanguage(language)) {
     return language;
   }
   return undefined;
diff --git a/src/overlay/index.test.ts b/src/overlay/index.test.ts
index 2d0b4d3fc..0db12f603 100644
--- a/src/overlay/index.test.ts
+++ b/src/overlay/index.test.ts
@@ -9,7 +9,7 @@ import * as actionsUtil from "../actions-util";
 import * as apiClient from "../api-client";
 import { ResolveDatabaseOutput } from "../codeql";
 import * as gitUtils from "../git-utils";
-import { KnownLanguage } from "../languages";
+import { BuiltInLanguage } from "../languages";
 import { getRunnerLogger } from "../logging";
 import {
   createTestConfig,
@@ -382,7 +382,7 @@ const testDownloadOverlayBaseDatabaseFromCache = test.macro({
       const testCase = { ...defaultDownloadTestCase, ...partialTestCase };
       const config = createTestConfig({
         dbLocation,
-        languages: [KnownLanguage.java],
+        languages: [BuiltInLanguage.java],
       });
 
       config.overlayDatabaseMode = testCase.overlayDatabaseMode;
diff --git a/src/start-proxy-action.ts b/src/start-proxy-action.ts
index 235970b47..a288acc5c 100644
--- a/src/start-proxy-action.ts
+++ b/src/start-proxy-action.ts
@@ -6,7 +6,7 @@ import * as core from "@actions/core";
 import * as actionsUtil from "./actions-util";
 import { getGitHubVersion } from "./api-client";
 import { Feature, FeatureEnablement, initFeatures } from "./feature-flags";
-import { KnownLanguage, parseBuiltInLanguage } from "./languages";
+import { BuiltInLanguage, parseBuiltInLanguage } from "./languages";
 import { getActionsLogger, Logger } from "./logging";
 import { getRepositoryNwo } from "./repository";
 import {
@@ -32,7 +32,7 @@ async function run(startedAt: Date) {
 
   const logger = getActionsLogger();
   let features: FeatureEnablement | undefined;
-  let language: KnownLanguage | undefined;
+  let language: BuiltInLanguage | undefined;
 
   try {
     // Make inputs accessible in the `post` step.
diff --git a/src/start-proxy.test.ts b/src/start-proxy.test.ts
index c5d452645..4d8f4afee 100644
--- a/src/start-proxy.test.ts
+++ b/src/start-proxy.test.ts
@@ -8,7 +8,7 @@ import sinon from "sinon";
 import * as apiClient from "./api-client";
 import * as defaults from "./defaults.json";
 import { setUpFeatureFlagTests } from "./feature-flags/testing-util";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { getRunnerLogger, Logger } from "./logging";
 import * as startProxyExports from "./start-proxy";
 import * as statusReport from "./status-report";
@@ -231,7 +231,7 @@ test("getCredentials filters by language when specified", async (t) => {
     getRunnerLogger(true),
     undefined,
     toEncodedJSON(mixedCredentials),
-    KnownLanguage.java,
+    BuiltInLanguage.java,
   );
   t.is(credentials.length, 1);
   t.is(credentials[0].type, "maven_repository");
@@ -242,7 +242,7 @@ test("getCredentials returns all for a language when specified", async (t) => {
     getRunnerLogger(true),
     undefined,
     toEncodedJSON(mixedCredentials),
-    KnownLanguage.go,
+    BuiltInLanguage.go,
   );
   t.is(credentials.length, 2);
 
@@ -262,7 +262,7 @@ test("getCredentials returns all goproxy_servers for Go when specified", async (
     getRunnerLogger(true),
     undefined,
     toEncodedJSON(multipleGoproxyServers),
-    KnownLanguage.go,
+    BuiltInLanguage.go,
   );
   t.is(credentials.length, 3);
 
@@ -291,7 +291,7 @@ test("getCredentials returns all maven_repositories for Java when specified", as
     getRunnerLogger(true),
     undefined,
     toEncodedJSON(multipleMavenRepositories),
-    KnownLanguage.java,
+    BuiltInLanguage.java,
   );
   t.is(credentials.length, 2);
 
@@ -479,7 +479,7 @@ test("getCredentials accepts OIDC configurations", (t) => {
     getRunnerLogger(true),
     undefined,
     toEncodedJSON(oidcConfigurations),
-    KnownLanguage.csharp,
+    BuiltInLanguage.csharp,
   );
   t.is(credentials.length, 3);
 
@@ -646,7 +646,7 @@ test("getCredentials returns all credentials for Actions when using LANGUAGE_TO_
     getRunnerLogger(true),
     undefined,
     credentialsInput,
-    KnownLanguage.actions,
+    BuiltInLanguage.actions,
     false,
   );
   t.is(credentials.length, mixedCredentials.length);
@@ -659,7 +659,7 @@ test("getCredentials returns no credentials for Actions when using NEW_LANGUAGE_
     getRunnerLogger(true),
     undefined,
     credentialsInput,
-    KnownLanguage.actions,
+    BuiltInLanguage.actions,
     true,
   );
   t.deepEqual(credentials, []);
diff --git a/src/start-proxy.ts b/src/start-proxy.ts
index 749a09a7c..8859eb16e 100644
--- a/src/start-proxy.ts
+++ b/src/start-proxy.ts
@@ -18,7 +18,7 @@ import {
   FeatureEnablement,
 } from "./feature-flags";
 import * as json from "./json";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { Logger } from "./logging";
 import {
   Address,
@@ -156,7 +156,7 @@ export function getSafeErrorMessage(error: Error): string {
 export async function sendFailedStatusReport(
   logger: Logger,
   startedAt: Date,
-  language: KnownLanguage | undefined,
+  language: BuiltInLanguage | undefined,
   unwrappedError: unknown,
 ) {
   const error = util.wrapError(unwrappedError);
@@ -195,7 +195,7 @@ function isPAT(value: string) {
   ]);
 }
 
-type RegistryMapping = Partial<Record<KnownLanguage, string[]>>;
+type RegistryMapping = Partial<Record<BuiltInLanguage, string[]>>;
 
 const LANGUAGE_TO_REGISTRY_TYPE: RegistryMapping = {
   java: ["maven_repository"],
@@ -327,7 +327,7 @@ export function getCredentials(
   logger: Logger,
   registrySecrets: string | undefined,
   registriesCredentials: string | undefined,
-  language: KnownLanguage | undefined,
+  language: BuiltInLanguage | undefined,
   skipUnusedRegistries: boolean = false,
 ): Credential[] {
   const registryMapping = skipUnusedRegistries
diff --git a/src/start-proxy/environment.test.ts b/src/start-proxy/environment.test.ts
index 6722c53ab..decd2fa6b 100644
--- a/src/start-proxy/environment.test.ts
+++ b/src/start-proxy/environment.test.ts
@@ -7,7 +7,7 @@ import * as io from "@actions/io";
 import test, { ExecutionContext } from "ava";
 import sinon from "sinon";
 
-import { JavaEnvVars, KnownLanguage } from "../languages";
+import { JavaEnvVars, BuiltInLanguage } from "../languages";
 import {
   checkExpectedLogMessages,
   getRecordingLogger,
@@ -182,11 +182,11 @@ test.serial("checkProxyEnvVars - credentials are removed from URLs", (t) => {
 });
 
 test.serial(
-  "checkProxyEnvironment - includes base checks for all known languages",
+  "checkProxyEnvironment - includes base checks for all built-in languages",
   async (t) => {
     stubToolrunner();
 
-    for (const language of Object.values(KnownLanguage)) {
+    for (const language of Object.values(BuiltInLanguage)) {
       const messages: LoggedMessage[] = [];
       const logger = getRecordingLogger(messages);
 
@@ -204,7 +204,7 @@ test.serial(
 
     stubToolrunner();
 
-    await checkProxyEnvironment(logger, KnownLanguage.java);
+    await checkProxyEnvironment(logger, BuiltInLanguage.java);
     assertEnvVarLogMessages(t, Object.keys(ProxyEnvVars), messages, false);
     assertEnvVarLogMessages(t, JAVA_PROXY_ENV_VARS, messages, false);
   },
diff --git a/src/start-proxy/environment.ts b/src/start-proxy/environment.ts
index 13eb12190..0a683cc07 100644
--- a/src/start-proxy/environment.ts
+++ b/src/start-proxy/environment.ts
@@ -4,7 +4,7 @@ import * as path from "path";
 import * as toolrunner from "@actions/exec/lib/toolrunner";
 import * as io from "@actions/io";
 
-import { JavaEnvVars, KnownLanguage, Language } from "../languages";
+import { JavaEnvVars, BuiltInLanguage, Language } from "../languages";
 import { Logger } from "../logging";
 import { getErrorMessage, isDefined } from "../util";
 
@@ -196,7 +196,7 @@ export async function checkProxyEnvironment(
 
   // Check language-specific configurations. If we don't know the language,
   // then we perform all checks.
-  if (language === undefined || language === KnownLanguage.java) {
+  if (language === undefined || language === BuiltInLanguage.java) {
     checkJavaEnvVars(logger);
 
     await showJavaSettings(logger);
diff --git a/src/status-report.test.ts b/src/status-report.test.ts
index 35d608b7d..8302e411f 100644
--- a/src/status-report.test.ts
+++ b/src/status-report.test.ts
@@ -4,7 +4,7 @@ import * as sinon from "sinon";
 import * as actionsUtil from "./actions-util";
 import { Config } from "./config-utils";
 import { EnvVar } from "./environment";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { getRunnerLogger } from "./logging";
 import { ToolsSource } from "./setup-codeql";
 import {
@@ -48,7 +48,7 @@ test.serial("createStatusReportBase", async (t) => {
       new Date("May 19, 2023 05:19:00"),
       createTestConfig({
         buildMode: BuildMode.None,
-        languages: [KnownLanguage.java, KnownLanguage.swift],
+        languages: [BuiltInLanguage.java, BuiltInLanguage.swift],
       }),
       { numAvailableBytes: 100, numTotalBytes: 500 },
       getRunnerLogger(false),
@@ -345,7 +345,7 @@ test.serial(
   "returns a value",
   createTestConfig({
     buildMode: BuildMode.None,
-    languages: [KnownLanguage.java, KnownLanguage.swift],
+    languages: [BuiltInLanguage.java, BuiltInLanguage.swift],
   }),
   {
     trap_cache_download_size_bytes: 1024,
@@ -360,7 +360,7 @@ test.serial(
   "includes packs for a single language",
   createTestConfig({
     buildMode: BuildMode.None,
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     computedConfig: {
       packs: ["foo", "bar"],
     },
@@ -377,7 +377,7 @@ test.serial(
   "includes packs for multiple languages",
   createTestConfig({
     buildMode: BuildMode.None,
-    languages: [KnownLanguage.java, KnownLanguage.swift],
+    languages: [BuiltInLanguage.java, BuiltInLanguage.swift],
     computedConfig: {
       packs: { java: ["java-foo", "java-bar"], swift: ["swift-bar"] },
     },
diff --git a/src/tracer-config.test.ts b/src/tracer-config.test.ts
index cc4995708..58f844b8e 100644
--- a/src/tracer-config.test.ts
+++ b/src/tracer-config.test.ts
@@ -6,7 +6,7 @@ import * as sinon from "sinon";
 
 import { CodeQL, getCodeQLForTesting } from "./codeql";
 import * as configUtils from "./config-utils";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { createTestConfig, makeVersionInfo, setupTests } from "./testing-utils";
 import { ToolsFeature } from "./tools-features";
 import { getCombinedTracerConfig } from "./tracer-config";
@@ -16,7 +16,7 @@ setupTests(test);
 
 function getTestConfig(tempDir: string): configUtils.Config {
   return createTestConfig({
-    languages: [KnownLanguage.java],
+    languages: [BuiltInLanguage.java],
     tempDir,
     dbLocation: path.resolve(tempDir, "codeql_databases"),
   });
@@ -36,7 +36,7 @@ async function stubCodeql(
     );
   sinon
     .stub(codeqlObject, "isTracedLanguage")
-    .withArgs(KnownLanguage.java)
+    .withArgs(BuiltInLanguage.java)
     .resolves(true);
   return codeqlObject;
 }
@@ -45,7 +45,7 @@ test("getCombinedTracerConfig - return undefined when no languages are traced la
   await util.withTmpDir(async (tmpDir) => {
     const config = getTestConfig(tmpDir);
     // No traced languages
-    config.languages = [KnownLanguage.javascript, KnownLanguage.python];
+    config.languages = [BuiltInLanguage.javascript, BuiltInLanguage.python];
     t.deepEqual(
       await getCombinedTracerConfig(await stubCodeql(), config),
       undefined,
diff --git a/src/trap-caching.test.ts b/src/trap-caching.test.ts
index a6c7fc76c..980547579 100644
--- a/src/trap-caching.test.ts
+++ b/src/trap-caching.test.ts
@@ -15,7 +15,7 @@ import {
 import * as configUtils from "./config-utils";
 import { Feature } from "./feature-flags";
 import * as gitUtils from "./git-utils";
-import { KnownLanguage } from "./languages";
+import { BuiltInLanguage } from "./languages";
 import { getRunnerLogger } from "./logging";
 import {
   createFeatures,
@@ -41,7 +41,7 @@ const stubCodeql = createStubCodeQL({
   async betterResolveLanguages() {
     return {
       extractors: {
-        [KnownLanguage.javascript]: [
+        [BuiltInLanguage.javascript]: [
           {
             extractor_root: "some_root",
             extractor_options: {
@@ -65,7 +65,7 @@ const stubCodeql = createStubCodeQL({
             },
           },
         ],
-        [KnownLanguage.cpp]: [
+        [BuiltInLanguage.cpp]: [
           {
             extractor_root: "other_root",
           },
@@ -76,7 +76,7 @@ const stubCodeql = createStubCodeQL({
 });
 
 const testConfigWithoutTmpDir = createTestConfig({
-  languages: [KnownLanguage.javascript, KnownLanguage.cpp],
+  languages: [BuiltInLanguage.javascript, BuiltInLanguage.cpp],
   trapCaches: {
     javascript: "/some/cache/dir",
   },
@@ -84,7 +84,7 @@ const testConfigWithoutTmpDir = createTestConfig({
 
 function getTestConfigWithTempDir(tempDir: string): configUtils.Config {
   return createTestConfig({
-    languages: [KnownLanguage.javascript, KnownLanguage.ruby],
+    languages: [BuiltInLanguage.javascript, BuiltInLanguage.ruby],
     tempDir,
     dbLocation: path.resolve(tempDir, "codeql_databases"),
     trapCaches: {
@@ -100,7 +100,7 @@ test.serial("check flags for JS, analyzing default branch", async (t) => {
     sinon.stub(gitUtils, "isAnalyzingDefaultBranch").resolves(true);
     const result = await getTrapCachingExtractorConfigArgsForLang(
       config,
-      KnownLanguage.javascript,
+      BuiltInLanguage.javascript,
     );
     t.deepEqual(result, [
       `-O=javascript.trap.cache.dir=${path.resolve(tmpDir, "jsCache")}`,
@@ -131,10 +131,10 @@ test("get languages that support TRAP caching", async (t) => {
   const logger = getRecordingLogger(loggedMessages);
   const languagesSupportingCaching = await getLanguagesSupportingCaching(
     stubCodeql,
-    [KnownLanguage.javascript, KnownLanguage.cpp],
+    [BuiltInLanguage.javascript, BuiltInLanguage.cpp],
     logger,
   );
-  t.deepEqual(languagesSupportingCaching, [KnownLanguage.javascript]);
+  t.deepEqual(languagesSupportingCaching, [BuiltInLanguage.javascript]);
 });
 
 test.serial("upload cache key contains right fields", async (t) => {
@@ -180,7 +180,7 @@ test.serial(
       );
       await downloadTrapCaches(
         stubCodeql,
-        [KnownLanguage.javascript, KnownLanguage.cpp],
+        [BuiltInLanguage.javascript, BuiltInLanguage.cpp],
         logger,
       );
       t.assert(