feat(i18n): strengthen output-language.md template to enforce language compliance

packages/cli/src/utils/languageUtils.test.ts

@@ -218,6 +218,43 @@ describe('languageUtils', () => {
         '<!-- qwen-code:llm-output-language: TestLanguage -->',
       );
     });
+
+    it('should use mandatory language rule instead of preference', () => {
+      writeOutputLanguageFile('Chinese');
+
+      const writtenContent = vi.mocked(fs.writeFileSync).mock
+        .calls[0][1] as string;
+      expect(writtenContent).toContain(
+        'You MUST always respond in **Chinese**',
+      );
+      expect(writtenContent).toContain(
+        'This is a mandatory requirement, not a preference.',
+      );
+      expect(writtenContent).not.toContain('Prefer responding');
+    });
+
+    it('should include exception clause for explicit user language requests', () => {
+      writeOutputLanguageFile('English');
+
+      const writtenContent = vi.mocked(fs.writeFileSync).mock
+        .calls[0][1] as string;
+      expect(writtenContent).toContain('## Exception');
+      expect(writtenContent).toContain(
+        "switch to the user's requested language for the remainder of the conversation",
+      );
+    });
+
+    it('should use the correct language name throughout the template', () => {
+      writeOutputLanguageFile('Japanese');
+
+      const writtenContent = vi.mocked(fs.writeFileSync).mock
+        .calls[0][1] as string;
+      expect(writtenContent).toContain(
+        'You MUST always respond in **Japanese**',
+      );
+      expect(writtenContent).toContain('## Rule');
+      expect(writtenContent).toContain('## Exception');
+    });
   });
 
   describe('updateOutputLanguageFile', () => {

packages/cli/src/utils/languageUtils.ts

@@ -89,17 +89,18 @@ function generateOutputLanguageFileContent(language: string): string {
   return `# Output language preference: ${language}
 <!-- ${LLM_OUTPUT_LANGUAGE_MARKER_PREFIX} ${safeLanguage} -->
 
-## Goal
-Prefer responding in **${language}** for normal assistant messages and explanations.
+## Rule
+You MUST always respond in **${language}** regardless of the user's input language.
+This is a mandatory requirement, not a preference.
+
+## Exception
+If the user **explicitly** requests a response in a specific language (e.g., "please reply in English", "用中文回答"), switch to the user's requested language for the remainder of the conversation.
 
 ## Keep technical artifacts unchanged
 Do **not** translate or rewrite:
 - Code blocks, CLI commands, file paths, stack traces, logs, JSON keys, identifiers
 - Exact quoted text from the user (keep quotes verbatim)
 
-## When a conflict exists
-If higher-priority instructions (system/developer) require a different behavior, follow them.
-
 ## Tool / system outputs
 Raw tool/system outputs may contain fixed-format English. Preserve them verbatim, and if needed, add a short **${language}** explanation below.
 `;