fix(@angular-devkit/build-angular): correctly set i18n subPath in webpack browser builder

The `subPath` option was not being properly applied when using the webpack-based browser builder.

Closes #30247

Author: alan-agius4

packages/angular_devkit/build_angular/src/utils/process-bundle.ts

@@ -192,10 +192,10 @@ export async function inlineLocales(options: InlineOptions) {
     if (!transformResult || !transformResult.code) {
       throw new Error(`Unknown error occurred processing bundle for "${options.filename}".`);
     }
-
+    const subPath = i18n.locales[locale].subPath;
     const outputPath = path.join(
       options.outputPath,
-      i18n.flatOutput ? '' : locale,
+      i18n.flatOutput ? '' : subPath,
       options.filename,
     );
     await fs.writeFile(outputPath, transformResult.code);
@@ -284,9 +284,10 @@ async function inlineLocalesDirect(ast: ParseResult, options: InlineOptions) {
       source: string;
       map: { file: string; sourceRoot?: string };
     };
+    const subPath = i18n.locales[locale].subPath;
     const outputPath = path.join(
       options.outputPath,
-      i18n.flatOutput ? '' : locale,
+      i18n.flatOutput ? '' : subPath,
       options.filename,
     );
     await fs.writeFile(outputPath, outputCode);
@@ -308,10 +309,11 @@ async function inlineCopyOnly(options: InlineOptions) {
     throw new Error('i18n options are missing');
   }
 
+  const subPath = i18n.locales[locale].subPath;
   for (const locale of i18n.inlineLocales) {
     const outputPath = path.join(
       options.outputPath,
-      i18n.flatOutput ? '' : locale,
+      i18n.flatOutput ? '' : subPath,
       options.filename,
     );
     await fs.writeFile(outputPath, options.code);

tests/legacy-cli/e2e/tests/i18n/ivy-localize-sub-path.ts

@@ -0,0 +1,78 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { join } from 'path';
+import { expectFileToMatch } from '../../utils/fs';
+import { ng } from '../../utils/process';
+import { updateJsonFile } from '../../utils/project';
+import { baseDir, baseHrefs, externalServer, langTranslations, setupI18nConfig } from './setup';
+
+export default async function () {
+  // Setup i18n tests and config.
+  await setupI18nConfig();
+
+  const URL_SUB_PATH: Record<string, string> = {
+    'en-US': '',
+    'fr': 'fr',
+    'de': 'deutsche',
+  };
+
+  // Update angular.json
+  await updateJsonFile('angular.json', (workspaceJson) => {
+    const appProject = workspaceJson.projects['test-project'];
+    // tslint:disable-next-line: no-any
+    const i18n: Record<string, any> = appProject.i18n;
+
+    i18n.sourceLocale = {
+      subPath: URL_SUB_PATH['en-US'],
+    };
+
+    i18n.locales['fr'] = {
+      translation: i18n.locales['fr'],
+      subPath: URL_SUB_PATH['fr'],
+    };
+
+    i18n.locales['de'] = {
+      translation: i18n.locales['de'],
+      subPath: URL_SUB_PATH['de'],
+    };
+  });
+
+  // Build each locale and verify the output.
+  await ng('build');
+  for (const { lang } of langTranslations) {
+    if (baseHrefs[lang] === undefined) {
+      throw new Error('Invalid E2E test setup: unexpected locale ' + lang);
+    }
+
+    const outputPath = join(baseDir, URL_SUB_PATH[lang]);
+
+    // Verify the HTML lang attribute is present
+    await expectFileToMatch(`${outputPath}/index.html`, `lang="${lang}"`);
+
+    // Verify the HTML base HREF attribute is present
+    await expectFileToMatch(`${outputPath}/index.html`, `href="${baseHrefs[lang] || '/'}"`);
+
+    // Execute Application E2E tests for a production build without dev server
+    const { server, port, url } = await externalServer(
+      outputPath,
+      (baseHrefs[lang] as string) || '/',
+    );
+    try {
+      await ng(
+        'e2e',
+        `--port=${port}`,
+        `--configuration=${lang}`,
+        '--dev-server-target=',
+        `--base-url=${url}`,
+      );
+    } finally {
+      server.close();
+    }
+  }
+}