diff --git a/packages/angular/build/src/tools/i18n/i18n-inliner-worker.ts b/packages/angular/build/src/tools/i18n/i18n-inliner-worker.ts
index 4286f33a1b41..778ca55bb814 100644
--- a/packages/angular/build/src/tools/i18n/i18n-inliner-worker.ts
+++ b/packages/angular/build/src/tools/i18n/i18n-inliner-worker.ts
@@ -11,6 +11,7 @@ import {
   type ɵParsedTranslation,
   ɵisMissingTranslationError,
   ɵmakeTemplateObject,
+  ɵparseMessage,
   ɵtranslate,
 } from '@angular/localize';
 import { MagicString } from 'magic-string';
@@ -335,11 +336,20 @@ type DiagnosticMessage = { type: 'error' | 'warning'; message: string };
  */
 function translateMessage(
   diagnostics: DiagnosticMessage[],
-  translations: Record<string, ɵParsedTranslation>,
+  translations: Record<string, ɵParsedTranslation> | undefined,
   messageParts: TemplateStringsArray,
   substitutions: readonly number[],
   missingTranslation: 'error' | 'warning' | 'ignore',
 ): [TemplateStringsArray, readonly number[]] {
+  // Fast path: untranslated locale (e.g. source locale without a translation dictionary).
+  // Directly parse the message parts to strip metadata and placeholder markers without
+  // throwing and catching a MissingTranslationError exception.
+  if (translations === undefined) {
+    const message = ɵparseMessage(messageParts, substitutions);
+
+    return [ɵmakeTemplateObject(message.messageParts, message.messageParts), substitutions];
+  }
+
   try {
     return ɵtranslate(translations, messageParts, substitutions) as [
       TemplateStringsArray,
@@ -512,7 +522,7 @@ async function inlineLocalize(
   for (const callSite of metadata.callSites) {
     const [translatedParts, translatedSubstitutions] = translateMessage(
       diagnostics,
-      translation || {},
+      translation,
       callSite.messageParts,
       callSite.expressionIndexes,
       translation === undefined ? 'ignore' : missingTranslation,
diff --git a/packages/angular/build/src/tools/i18n/i18n-inliner_spec.ts b/packages/angular/build/src/tools/i18n/i18n-inliner_spec.ts
index bbc827b94c7f..2fbb6e02ce31 100644
--- a/packages/angular/build/src/tools/i18n/i18n-inliner_spec.ts
+++ b/packages/angular/build/src/tools/i18n/i18n-inliner_spec.ts
@@ -136,6 +136,20 @@ describe('I18nInliner', () => {
     expect(findFile(outputFiles, 'main.js').text).toContain('"Hello"');
   });
 
+  it('retains the original messages with placeholders for a locale without translations', async () => {
+    const source = 'export const greeting = $localize`:@@greeting:Hello ${name}:NAME:!`;\n';
+    const { outputFiles, errors, warnings } = await createInliner().inlineForLocale(
+      [browserFile('main.js', source)],
+      'en-US',
+      undefined,
+    );
+
+    expect(errors).toEqual([]);
+    expect(warnings).toEqual([]);
+    expect(findFile(outputFiles, 'main.js').text).toContain('`Hello ${name}!`');
+    expect(findFile(outputFiles, 'main.js').text).not.toContain('$localize');
+  });
+
   it('warns and retains the original message when a locale is missing a translation', async () => {
     const { outputFiles, errors, warnings } = await createInliner().inlineForLocale(
       [browserFile('main.js', GREETING_SOURCE)],
diff --git a/scripts/benchmarks/i18n/scenarios.mts b/scripts/benchmarks/i18n/scenarios.mts
index aaebdfd47cf7..5cb16f654d51 100644
--- a/scripts/benchmarks/i18n/scenarios.mts
+++ b/scripts/benchmarks/i18n/scenarios.mts
@@ -541,6 +541,113 @@ export function createLargeEnterpriseScenario(
   };
 }
 
+/**
+ * 7. Massive Multichunk Scenario:
+ * 800 chunks total (~150 MB JS): 1 main bundle (6 MB) + 250 small chunks (40 KB) + 549 feature chunks (245 KB),
+ * 8 locales, 5,000 translations, sourcemaps ON.
+ * Stresses worker thread pool queue capacity, dispatch throughput, IPC messaging, and memory reclamation
+ * across hundreds of parallel files.
+ */
+export function createMassiveMultichunkScenario(
+  options: ScenarioFactoryOptions = {},
+): BenchmarkScenario {
+  let workload: GeneratedWorkload | undefined;
+
+  return {
+    name: 'massive-multichunk',
+    description: 'Massive Multichunk: 800 chunks (~150 MB JS), 8 locales, sourcemaps ON',
+    get inputSizeBytes() {
+      return workload?.totalInputSizeBytes ?? 0;
+    },
+    get localeCount() {
+      return DEFAULT_LOCALES_8.length;
+    },
+    async setup() {
+      await initializeFixtures();
+      const files: BuildOutputFile[] = [];
+      const totalMessages = 5000;
+      let messageOffset = 0;
+
+      // 1. Dominant entry bundle: 6 MB, 1,000 messages
+      const mainMessages = 1000;
+      const { codeFile: mainCode, mapFile: mainMap } = generateSyntheticBundle({
+        filename: 'main.js',
+        targetByteSize: 6 * 1024 * 1024,
+        messageCount: mainMessages,
+        withSourceMap: true,
+        messageIdOffset: messageOffset,
+      });
+      files.push(mainCode);
+      if (mainMap) {
+        files.push(mainMap);
+      }
+      messageOffset += mainMessages;
+
+      // 2. Small route/dialog chunks (< 100 KB): 250 chunks x 40 KB = 10 MB, 1,000 messages (4 msgs/chunk)
+      const smallChunkCount = 250;
+      const smallChunkSizeBytes = 40 * 1024;
+      const smallChunkMessages = 4;
+      for (let i = 0; i < smallChunkCount; i++) {
+        const { codeFile, mapFile } = generateSyntheticBundle({
+          filename: `small_chunk_${i}.js`,
+          targetByteSize: smallChunkSizeBytes,
+          messageCount: smallChunkMessages,
+          withSourceMap: true,
+          messageIdOffset: messageOffset + i * smallChunkMessages,
+        });
+        files.push(codeFile);
+        if (mapFile) {
+          files.push(mapFile);
+        }
+      }
+      messageOffset += smallChunkCount * smallChunkMessages;
+
+      // 3. Medium/large feature chunks: 549 chunks x 245 KB = ~134.5 MB, 3,000 messages
+      const featureChunkCount = 549;
+      const featureChunkSizeBytes = 245 * 1024;
+      const remainingMessages = totalMessages - messageOffset;
+      const messagesPerFeatureChunk = Math.max(
+        1,
+        Math.floor(remainingMessages / featureChunkCount),
+      );
+      for (let i = 0; i < featureChunkCount; i++) {
+        const { codeFile, mapFile } = generateSyntheticBundle({
+          filename: `feature_chunk_${i}.js`,
+          targetByteSize: featureChunkSizeBytes,
+          messageCount: messagesPerFeatureChunk,
+          withSourceMap: true,
+          messageIdOffset: messageOffset + i * messagesPerFeatureChunk,
+        });
+        files.push(codeFile);
+        if (mapFile) {
+          files.push(mapFile);
+        }
+      }
+
+      const locales = generateTranslations(DEFAULT_LOCALES_8, totalMessages);
+      workload = {
+        files,
+        locales,
+        totalInputSizeBytes: calculateInputSizeBytes(files),
+      };
+    },
+    async run() {
+      if (!workload) {
+        return;
+      }
+      const inliner = new I18nInliner({
+        missingTranslation: 'warning',
+        maxConcurrency: options.concurrency,
+      });
+      try {
+        await inliner.inlineAll(workload.files, workload.locales);
+      } finally {
+        await inliner.close();
+      }
+    },
+  };
+}
+
 export function getAllScenarios(options: ScenarioFactoryOptions = {}): BenchmarkScenario[] {
   return [
     createStandardAppScenario(options),
@@ -549,6 +656,7 @@ export function getAllScenarios(options: ScenarioFactoryOptions = {}): Benchmark
     createLargeEnterpriseScenario(options),
     createMonolithicScenario(options),
     createMultiDominantScenario(options),
+    createMassiveMultichunkScenario(options),
     createPersistentCacheWarmScenario(options),
   ];
 }