feat: adjust code

feat(i18n): auto-detect LLM output language from system locale

docs/users/features/_meta.ts

@@ -9,4 +9,5 @@ export default {
   mcp: 'MCP',
   'token-caching': 'Token Caching',
   sandbox: 'Sandboxing',
+  language: 'i18n',
 };

docs/users/features/commands.md

@@ -48,7 +48,7 @@ Commands specifically for controlling interface and output language.
 | → `ui [language]`     | Set UI interface language        | `/language ui zh-CN`       |
 | → `output [language]` | Set LLM output language          | `/language output Chinese` |
 
-- Available UI languages: `zh-CN` (Simplified Chinese), `en-US` (English)
+- Available built-in UI languages: `zh-CN` (Simplified Chinese), `en-US` (English), `ru-RU` (Russian), `de-DE` (German)
 - Output language examples: `Chinese`, `English`, `Japanese`, etc.
 
 ### 1.4 Tool and Model Management
@@ -72,17 +72,16 @@ Commands for managing AI tools and models.
 
 Commands for obtaining information and performing system settings.
 
-| Command         | Description                                     | Usage Examples                                   |
-| --------------- | ----------------------------------------------- | ------------------------------------------------ |
-| `/help`         | Display help information for available commands | `/help` or `/?`                                  |
-| `/about`        | Display version information                     | `/about`                                         |
-| `/stats`        | Display detailed statistics for current session | `/stats`                                         |
-| `/settings`     | Open settings editor                            | `/settings`                                      |
-| `/auth`         | Change authentication method                    | `/auth`                                          |
-| `/bug`          | Submit issue about Qwen Code                    | `/bug Button click unresponsive`                 |
-| `/copy`         | Copy last output content to clipboard           | `/copy`                                          |
-| `/quit-confirm` | Show confirmation dialog before quitting        | `/quit-confirm` (shortcut: press `Ctrl+C` twice) |
-| `/quit`         | Exit Qwen Code immediately                      | `/quit` or `/exit`                               |
+| Command     | Description                                     | Usage Examples                   |
+| ----------- | ----------------------------------------------- | -------------------------------- |
+| `/help`     | Display help information for available commands | `/help` or `/?`                  |
+| `/about`    | Display version information                     | `/about`                         |
+| `/stats`    | Display detailed statistics for current session | `/stats`                         |
+| `/settings` | Open settings editor                            | `/settings`                      |
+| `/auth`     | Change authentication method                    | `/auth`                          |
+| `/bug`      | Submit issue about Qwen Code                    | `/bug Button click unresponsive` |
+| `/copy`     | Copy last output content to clipboard           | `/copy`                          |
+| `/quit`     | Exit Qwen Code immediately                      | `/quit` or `/exit`               |
 
 ### 1.6 Common Shortcuts
 

docs/users/features/language.md

@@ -0,0 +1,136 @@
+# Internationalization (i18n) & Language
+
+Qwen Code is built for multilingual workflows: it supports UI localization (i18n/l10n) in the CLI, lets you choose the assistant output language, and allows custom UI language packs.
+
+## Overview
+
+From a user point of view, Qwen Code’s “internationalization” spans multiple layers:
+
+| Capability / Setting     | What it controls                                                       | Where stored                 |
+| ------------------------ | ---------------------------------------------------------------------- | ---------------------------- |
+| `/language ui`           | Terminal UI text (menus, system messages, prompts)                     | `~/.qwen/settings.json`      |
+| `/language output`       | Language the AI responds in (an output preference, not UI translation) | `~/.qwen/output-language.md` |
+| Custom UI language packs | Overrides/extends built-in UI translations                             | `~/.qwen/locales/*.js`       |
+
+## UI Language
+
+This is the CLI’s UI localization layer (i18n/l10n): it controls the language of menus, prompts, and system messages.
+
+### Setting the UI Language
+
+Use the `/language ui` command:
+
+```bash
+/language ui zh-CN    # Chinese
+/language ui en-US    # English
+/language ui ru-RU    # Russian
+/language ui de-DE    # German
+```
+
+Aliases are also supported:
+
+```bash
+/language ui zh       # Chinese
+/language ui en       # English
+/language ui ru       # Russian
+/language ui de       # German
+```
+
+### Auto-detection
+
+On first startup, Qwen Code detects your system locale and sets the UI language automatically.
+
+Detection priority:
+
+1. `QWEN_CODE_LANG` environment variable
+2. `LANG` environment variable
+3. System locale via JavaScript Intl API
+4. Default: English
+
+## LLM Output Language
+
+The LLM output language controls what language the AI assistant responds in, regardless of what language you type your questions in.
+
+### How It Works
+
+The LLM output language is controlled by a rule file at `~/.qwen/output-language.md`. This file is automatically included in the LLM's context during startup, instructing it to respond in the specified language.
+
+### Auto-detection
+
+On first startup, if no `output-language.md` file exists, Qwen Code automatically creates one based on your system locale. For example:
+
+- System locale `zh` creates a rule for Chinese responses
+- System locale `en` creates a rule for English responses
+- System locale `ru` creates a rule for Russian responses
+- System locale `de` creates a rule for German responses
+
+### Manual Setting
+
+Use `/language output <language>` to change:
+
+```bash
+/language output Chinese
+/language output English
+/language output Japanese
+/language output German
+```
+
+Any language name works. The LLM will be instructed to respond in that language.
+
+> [!note]
+>
+> After changing the output language, restart Qwen Code for the change to take effect.
+
+### File Location
+
+```
+~/.qwen/output-language.md
+```
+
+## Configuration
+
+### Via Settings Dialog
+
+1. Run `/settings`
+2. Find "Language" under General
+3. Select your preferred UI language
+
+### Via Environment Variable
+
+```bash
+export QWEN_CODE_LANG=zh
+```
+
+This influences auto-detection on first startup (if you haven’t set a UI language and no `output-language.md` file exists yet).
+
+## Custom Language Packs
+
+For UI translations, you can create custom language packs in `~/.qwen/locales/`:
+
+- Example: `~/.qwen/locales/es.js` for Spanish
+- Example: `~/.qwen/locales/fr.js` for French
+
+User directory takes precedence over built-in translations.
+
+> [!tip]
+>
+> Contributions are welcome! If you’d like to improve built-in translations or add new languages.
+> For a concrete example, see [PR #1238: feat(i18n): add Russian language support](https://github.com/QwenLM/qwen-code/pull/1238).
+
+### Language Pack Format
+
+```javascript
+// ~/.qwen/locales/es.js
+export default {
+  Hello: 'Hola',
+  Settings: 'Configuracion',
+  // ... more translations
+};
+```
+
+## Related Commands
+
+- `/language` - Show current language settings
+- `/language ui [lang]` - Set UI language
+- `/language output <language>` - Set LLM output language
+- `/settings` - Open settings dialog

packages/cli/src/core/initializer.ts

@@ -15,6 +15,7 @@ import { type LoadedSettings, SettingScope } from '../config/settings.js';
 import { performInitialAuth } from './auth.js';
 import { validateTheme } from './theme.js';
 import { initializeI18n } from '../i18n/index.js';
+import { initializeLlmOutputLanguage } from '../ui/commands/languageCommand.js';
 
 export interface InitializationResult {
   authError: string | null;
@@ -41,6 +42,9 @@ export async function initializeApp(
     'auto';
   await initializeI18n(languageSetting);
 
+  // Auto-detect and set LLM output language on first use
+  initializeLlmOutputLanguage();
+
   const authType = settings.merged.security?.auth?.selectedType;
   const authError = await performInitialAuth(config, authType);
 

packages/cli/src/i18n/index.ts

@@ -1,6 +1,6 @@
 /**
  * @license
- * Copyright 2025 Qwen
+ * Copyright 2025 Qwen team
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -8,8 +8,13 @@ import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { fileURLToPath, pathToFileURL } from 'node:url';
 import { homedir } from 'node:os';
+import {
+  type SupportedLanguage,
+  getLanguageNameFromLocale,
+} from './languages.js';
 
-export type SupportedLanguage = 'en' | 'zh' | 'ru' | string; // Allow custom language codes
+export type { SupportedLanguage };
+export { getLanguageNameFromLocale };
 
 // State
 let currentLanguage: SupportedLanguage = 'en';
@@ -52,11 +57,13 @@ export function detectSystemLanguage(): SupportedLanguage {
   if (envLang?.startsWith('zh')) return 'zh';
   if (envLang?.startsWith('en')) return 'en';
   if (envLang?.startsWith('ru')) return 'ru';
+  if (envLang?.startsWith('de')) return 'de';
 
   try {
     const locale = Intl.DateTimeFormat().resolvedOptions().locale;
     if (locale.startsWith('zh')) return 'zh';
     if (locale.startsWith('ru')) return 'ru';
+    if (locale.startsWith('de')) return 'de';
   } catch {
     // Fallback to default
   }

packages/cli/src/i18n/languages.ts

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2025 Qwen team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+export type SupportedLanguage = 'en' | 'zh' | 'ru' | 'de' | string;
+
+export interface LanguageDefinition {
+  /** The internal locale code used by the i18n system (e.g., 'en', 'zh'). */
+  code: SupportedLanguage;
+  /** The standard name used in UI settings (e.g., 'en-US', 'zh-CN'). */
+  id: string;
+  /** The full English name of the language (e.g., 'English', 'Chinese'). */
+  fullName: string;
+}
+
+export const SUPPORTED_LANGUAGES: readonly LanguageDefinition[] = [
+  {
+    code: 'en',
+    id: 'en-US',
+    fullName: 'English',
+  },
+  {
+    code: 'zh',
+    id: 'zh-CN',
+    fullName: 'Chinese',
+  },
+  {
+    code: 'ru',
+    id: 'ru-RU',
+    fullName: 'Russian',
+  },
+  {
+    code: 'de',
+    id: 'de-DE',
+    fullName: 'German',
+  },
+];
+
+/**
+ * Maps a locale code to its English language name.
+ * Used for LLM output language instructions.
+ */
+export function getLanguageNameFromLocale(locale: SupportedLanguage): string {
+  const lang = SUPPORTED_LANGUAGES.find((l) => l.code === locale);
+  return lang?.fullName || 'English';
+}

packages/cli/src/ui/commands/languageCommand.test.ts

@@ -13,6 +13,16 @@ import { createMockCommandContext } from '../../test-utils/mockCommandContext.js
 vi.mock('../../i18n/index.js', () => ({
   setLanguageAsync: vi.fn().mockResolvedValue(undefined),
   getCurrentLanguage: vi.fn().mockReturnValue('en'),
+  detectSystemLanguage: vi.fn().mockReturnValue('en'),
+  getLanguageNameFromLocale: vi.fn((locale: string) => {
+    const map: Record<string, string> = {
+      zh: 'Chinese',
+      en: 'English',
+      ru: 'Russian',
+      de: 'German',
+    };
+    return map[locale] || 'English';
+  }),
   t: vi.fn((key: string) => key),
 }));
 
@@ -61,7 +71,10 @@ vi.mock('@qwen-code/qwen-code-core', async (importOriginal) => {
 
 // Import modules after mocking
 import * as i18n from '../../i18n/index.js';
-import { languageCommand } from './languageCommand.js';
+import {
+  languageCommand,
+  initializeLlmOutputLanguage,
+} from './languageCommand.js';
 
 describe('languageCommand', () => {
   let mockContext: CommandContext;
@@ -186,6 +199,39 @@ describe('languageCommand', () => {
         content: expect.stringContaining('Chinese'),
       });
     });
+
+    it('should parse Unicode LLM output language from marker', async () => {
+      vi.mocked(fs.existsSync).mockReturnValue(true);
+      vi.mocked(fs.readFileSync).mockReturnValue(
+        [
+          '# ⚠️ CRITICAL: 中文 Output Language Rule - HIGHEST PRIORITY ⚠️',
+          '<!-- qwen-code:llm-output-language: 中文 -->',
+          '',
+          'Some other content...',
+        ].join('\n'),
+      );
+
+      vi.mocked(i18n.t).mockImplementation(
+        (key: string, params?: Record<string, string>) => {
+          if (params && key.includes('{{lang}}')) {
+            return key.replace('{{lang}}', params['lang'] || '');
+          }
+          return key;
+        },
+      );
+
+      if (!languageCommand.action) {
+        throw new Error('The language command must have an action.');
+      }
+
+      const result = await languageCommand.action(mockContext, '');
+
+      expect(result).toEqual({
+        type: 'message',
+        messageType: 'info',
+        content: expect.stringContaining('中文'),
+      });
+    });
   });
 
   describe('main command action - config not available', () => {
@@ -400,6 +446,34 @@ describe('languageCommand', () => {
       });
     });
 
+    it('should normalize locale code "ru" to "Russian"', async () => {
+      if (!languageCommand.action) {
+        throw new Error('The language command must have an action.');
+      }
+
+      await languageCommand.action(mockContext, 'output ru');
+
+      expect(fs.writeFileSync).toHaveBeenCalledWith(
+        expect.stringContaining('output-language.md'),
+        expect.stringContaining('Russian'),
+        'utf-8',
+      );
+    });
+
+    it('should normalize locale code "de" to "German"', async () => {
+      if (!languageCommand.action) {
+        throw new Error('The language command must have an action.');
+      }
+
+      await languageCommand.action(mockContext, 'output de');
+
+      expect(fs.writeFileSync).toHaveBeenCalledWith(
+        expect.stringContaining('output-language.md'),
+        expect.stringContaining('German'),
+        'utf-8',
+      );
+    });
+
     it('should handle file write errors gracefully', async () => {
       vi.mocked(fs.writeFileSync).mockImplementation(() => {
         throw new Error('Permission denied');
@@ -481,6 +555,8 @@ describe('languageCommand', () => {
       const nestedNames = uiSubcommand?.subCommands?.map((c) => c.name);
       expect(nestedNames).toContain('zh-CN');
       expect(nestedNames).toContain('en-US');
+      expect(nestedNames).toContain('ru-RU');
+      expect(nestedNames).toContain('de-DE');
     });
 
     it('should have action that sets language', async () => {
@@ -542,6 +618,9 @@ describe('languageCommand', () => {
     const enUSSubcommand = uiSubcommand?.subCommands?.find(
       (c) => c.name === 'en-US',
     );
+    const deDESubcommand = uiSubcommand?.subCommands?.find(
+      (c) => c.name === 'de-DE',
+    );
 
     it('zh-CN should have aliases', () => {
       expect(zhCNSubcommand?.altNames).toContain('zh');
@@ -553,6 +632,12 @@ describe('languageCommand', () => {
       expect(enUSSubcommand?.altNames).toContain('english');
     });
 
+    it('de-DE should have aliases', () => {
+      expect(deDESubcommand?.altNames).toContain('de');
+      expect(deDESubcommand?.altNames).toContain('german');
+      expect(deDESubcommand?.altNames).toContain('deutsch');
+    });
+
     it('zh-CN action should set Chinese', async () => {
       if (!zhCNSubcommand?.action) {
         throw new Error('zh-CN subcommand must have an action.');
@@ -583,6 +668,21 @@ describe('languageCommand', () => {
       });
     });
 
+    it('de-DE action should set German', async () => {
+      if (!deDESubcommand?.action) {
+        throw new Error('de-DE subcommand must have an action.');
+      }
+
+      const result = await deDESubcommand.action(mockContext, '');
+
+      expect(i18n.setLanguageAsync).toHaveBeenCalledWith('de');
+      expect(result).toEqual({
+        type: 'message',
+        messageType: 'info',
+        content: expect.stringContaining('UI language changed'),
+      });
+    });
+
     it('should reject extra arguments', async () => {
       if (!zhCNSubcommand?.action) {
         throw new Error('zh-CN subcommand must have an action.');
@@ -597,4 +697,74 @@ describe('languageCommand', () => {
       });
     });
   });
+
+  describe('initializeLlmOutputLanguage', () => {
+    beforeEach(() => {
+      vi.clearAllMocks();
+      vi.mocked(fs.existsSync).mockReturnValue(false);
+      vi.mocked(fs.mkdirSync).mockImplementation(() => undefined);
+      vi.mocked(fs.writeFileSync).mockImplementation(() => undefined);
+    });
+
+    it('should create file when it does not exist', () => {
+      vi.mocked(fs.existsSync).mockReturnValue(false);
+      vi.mocked(i18n.detectSystemLanguage).mockReturnValue('en');
+
+      initializeLlmOutputLanguage();
+
+      expect(fs.mkdirSync).toHaveBeenCalled();
+      expect(fs.writeFileSync).toHaveBeenCalledWith(
+        expect.stringContaining('output-language.md'),
+        expect.stringContaining('English'),
+        'utf-8',
+      );
+    });
+
+    it('should NOT overwrite existing file', () => {
+      vi.mocked(fs.existsSync).mockReturnValue(true);
+
+      initializeLlmOutputLanguage();
+
+      expect(fs.writeFileSync).not.toHaveBeenCalled();
+    });
+
+    it('should detect Chinese locale and create Chinese rule file', () => {
+      vi.mocked(fs.existsSync).mockReturnValue(false);
+      vi.mocked(i18n.detectSystemLanguage).mockReturnValue('zh');
+
+      initializeLlmOutputLanguage();
+
+      expect(fs.writeFileSync).toHaveBeenCalledWith(
+        expect.stringContaining('output-language.md'),
+        expect.stringContaining('Chinese'),
+        'utf-8',
+      );
+    });
+
+    it('should detect Russian locale and create Russian rule file', () => {
+      vi.mocked(fs.existsSync).mockReturnValue(false);
+      vi.mocked(i18n.detectSystemLanguage).mockReturnValue('ru');
+
+      initializeLlmOutputLanguage();
+
+      expect(fs.writeFileSync).toHaveBeenCalledWith(
+        expect.stringContaining('output-language.md'),
+        expect.stringContaining('Russian'),
+        'utf-8',
+      );
+    });
+
+    it('should detect German locale and create German rule file', () => {
+      vi.mocked(fs.existsSync).mockReturnValue(false);
+      vi.mocked(i18n.detectSystemLanguage).mockReturnValue('de');
+
+      initializeLlmOutputLanguage();
+
+      expect(fs.writeFileSync).toHaveBeenCalledWith(
+        expect.stringContaining('output-language.md'),
+        expect.stringContaining('German'),
+        'utf-8',
+      );
+    });
+  });
 });

packages/cli/src/ui/commands/languageCommand.ts

@@ -1,6 +1,6 @@
 /**
  * @license
- * Copyright 2025 Google LLC
+ * Copyright 2025 Qwen team
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -15,51 +15,72 @@ import { SettingScope } from '../../config/settings.js';
 import {
   setLanguageAsync,
   getCurrentLanguage,
+  detectSystemLanguage,
+  getLanguageNameFromLocale,
   type SupportedLanguage,
   t,
 } from '../../i18n/index.js';
+import {
+  SUPPORTED_LANGUAGES,
+  type LanguageDefinition,
+} from '../../i18n/languages.js';
 import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { Storage } from '@qwen-code/qwen-code-core';
 
 const LLM_OUTPUT_LANGUAGE_RULE_FILENAME = 'output-language.md';
+const LLM_OUTPUT_LANGUAGE_MARKER_PREFIX = 'qwen-code:llm-output-language:';
+
+function parseUiLanguageArg(input: string): SupportedLanguage | null {
+  const lowered = input.trim().toLowerCase();
+  if (!lowered) return null;
+  for (const lang of SUPPORTED_LANGUAGES) {
+    if (
+      lowered === lang.code ||
+      lowered === lang.id.toLowerCase() ||
+      lowered === lang.fullName.toLowerCase()
+    ) {
+      return lang.code;
+    }
+  }
+  return null;
+}
+
+function formatUiLanguageDisplay(lang: SupportedLanguage): string {
+  const option = SUPPORTED_LANGUAGES.find((o) => o.code === lang);
+  return option ? `${option.fullName}（${option.id}）` : lang;
+}
+
+function sanitizeLanguageForMarker(language: string): string {
+  // HTML comments cannot contain "--" or end marker "-->" safely.
+  // Also avoid newlines to keep the marker single-line and robust to parsing.
+  return language
+    .replace(/[\r\n]/g, ' ')
+    .replace(/-->/g, '')
+    .replace(/--/g, '');
+}
 
 /**
  * Generates the LLM output language rule template based on the language name.
  */
 function generateLlmOutputLanguageRule(language: string): string {
-  return `# ⚠️ CRITICAL: ${language} Output Language Rule - HIGHEST PRIORITY ⚠️
+  const markerLanguage = sanitizeLanguageForMarker(language);
+  return `# Output language preference: ${language}
+<!-- ${LLM_OUTPUT_LANGUAGE_MARKER_PREFIX} ${markerLanguage} -->
 
-## 🚨 MANDATORY RULE - NO EXCEPTIONS 🚨
+## Goal
+Prefer responding in **${language}** for normal assistant messages and explanations.
 
-**YOU MUST RESPOND IN ${language.toUpperCase()} FOR EVERY SINGLE OUTPUT, REGARDLESS OF THE USER'S INPUT LANGUAGE.**
+## 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)
 
-This is a **NON-NEGOTIABLE** requirement. Even if the user writes in English, says "hi", asks a simple question, or explicitly requests another language, **YOU MUST ALWAYS RESPOND IN ${language.toUpperCase()}.**
+## When a conflict exists
+If higher-priority instructions (system/developer) require a different behavior, follow them.
 
-## What Must Be in ${language}
-
-**EVERYTHING** you output: conversation replies, tool call descriptions, success/error messages, generated file content (comments, documentation), and all explanatory text.
-
-**Tool outputs**: All descriptive text from \`read_file\`, \`write_file\`, \`codebase_search\`, \`run_terminal_cmd\`, \`todo_write\`, \`web_search\`, etc. MUST be in ${language}.
-
-## Examples
-
-### ✅ CORRECT:
-- User says "hi" → Respond in ${language} (e.g., "Bonjour" if ${language} is French)
-- Tool result → "已成功读取文件 config.json" (if ${language} is Chinese)
-- Error → "无法找到指定的文件" (if ${language} is Chinese)
-
-### ❌ WRONG:
-- User says "hi" → "Hello" in English
-- Tool result → "Successfully read file" in English
-- Error → "File not found" in English
-
-## Notes
-
-- Code elements (variable/function names, syntax) can remain in English
-- Comments, documentation, and all other text MUST be in ${language}
-
-**THIS RULE IS ACTIVE NOW. ALL OUTPUTS MUST BE IN ${language.toUpperCase()}. NO EXCEPTIONS.**
+## Tool / system outputs
+Raw tool/system outputs may contain fixed-format English. Preserve them verbatim, and if needed, add a short **${language}** explanation below.
 `;
 }
 
@@ -73,6 +94,80 @@ function getLlmOutputLanguageRulePath(): string {
   );
 }
 
+/**
+ * Normalizes a language input to its full English name.
+ * If the input is a known locale code (e.g., "ru", "zh"), converts it to the full name.
+ * Otherwise, returns the input as-is (e.g., "Japanese" stays "Japanese").
+ */
+function normalizeLanguageName(language: string): string {
+  const lowered = language.toLowerCase();
+  // Check if it's a known locale code and convert to full name
+  const fullName = getLanguageNameFromLocale(lowered);
+  // If getLanguageNameFromLocale returned a different value, use it
+  // Otherwise, use the original input (preserves case for unknown languages)
+  if (fullName !== 'English' || lowered === 'en') {
+    return fullName;
+  }
+  return language;
+}
+
+function extractLlmOutputLanguageFromRuleFileContent(
+  content: string,
+): string | null {
+  // Preferred: machine-readable marker that supports Unicode and spaces.
+  // Example: <!-- qwen-code:llm-output-language: 中文 -->
+  const markerMatch = content.match(
+    new RegExp(
+      String.raw`<!--\s*${LLM_OUTPUT_LANGUAGE_MARKER_PREFIX}\s*(.*?)\s*-->`,
+      'i',
+    ),
+  );
+  if (markerMatch?.[1]) {
+    const lang = markerMatch[1].trim();
+    if (lang) return lang;
+  }
+
+  // Backward compatibility: parse the heading line.
+  // Example: "# CRITICAL: Chinese Output Language Rule - HIGHEST PRIORITY"
+  // Example: "# ⚠️ CRITICAL: 日本語 Output Language Rule - HIGHEST PRIORITY ⚠️"
+  const headingMatch = content.match(
+    /^#.*?CRITICAL:\s*(.*?)\s+Output Language Rule\b/im,
+  );
+  if (headingMatch?.[1]) {
+    const lang = headingMatch[1].trim();
+    if (lang) return lang;
+  }
+
+  return null;
+}
+
+/**
+ * Initializes the LLM output language rule file on first startup.
+ * If the file already exists, it is not overwritten (respects user preference).
+ */
+export function initializeLlmOutputLanguage(): void {
+  const filePath = getLlmOutputLanguageRulePath();
+
+  // Skip if file already exists (user preference)
+  if (fs.existsSync(filePath)) {
+    return;
+  }
+
+  // Detect system language and map to language name
+  const detectedLocale = detectSystemLanguage();
+  const languageName = getLanguageNameFromLocale(detectedLocale);
+
+  // Generate the rule file
+  const content = generateLlmOutputLanguageRule(languageName);
+
+  // Ensure directory exists
+  const dir = path.dirname(filePath);
+  fs.mkdirSync(dir, { recursive: true });
+
+  // Write file
+  fs.writeFileSync(filePath, content, 'utf-8');
+}
+
 /**
  * Gets the current LLM output language from the rule file if it exists.
  */
@@ -81,12 +176,7 @@ function getCurrentLlmOutputLanguage(): string | null {
   if (fs.existsSync(filePath)) {
     try {
       const content = fs.readFileSync(filePath, 'utf-8');
-      // Extract language name from the first line
-      // Template format: "# CRITICAL: Chinese Output Language Rule - HIGHEST PRIORITY"
-      const match = content.match(/^#.*?(\w+)\s+Output Language Rule/i);
-      if (match) {
-        return match[1];
-      }
+      return extractLlmOutputLanguageFromRuleFileContent(content);
     } catch {
       // Ignore errors
     }
@@ -127,18 +217,11 @@ async function setUiLanguage(
   // Reload commands to update their descriptions with the new language
   context.ui.reloadCommands();
 
-  // Map language codes to friendly display names
-  const langDisplayNames: Partial<Record<SupportedLanguage, string>> = {
-    zh: '中文（zh-CN）',
-    en: 'English（en-US）',
-    ru: 'Русский (ru-RU)',
-  };
-
   return {
     type: 'message',
     messageType: 'info',
     content: t('UI language changed to {{lang}}', {
-      lang: langDisplayNames[lang] || lang,
+      lang: formatUiLanguageDisplay(lang),
     }),
   };
 }
@@ -151,7 +234,9 @@ function generateLlmOutputLanguageRuleFile(
 ): Promise<MessageActionReturn> {
   try {
     const filePath = getLlmOutputLanguageRulePath();
-    const content = generateLlmOutputLanguageRule(language);
+    // Normalize locale codes (e.g., "ru" -> "Russian") to full language names
+    const normalizedLanguage = normalizeLanguageName(language);
+    const content = generateLlmOutputLanguageRule(normalizedLanguage);
 
     // Ensure directory exists
     const dir = path.dirname(filePath);
@@ -195,16 +280,6 @@ export const languageCommand: SlashCommand = {
     context: CommandContext,
     args: string,
   ): Promise<SlashCommandActionReturn> => {
-    const { services } = context;
-
-    if (!services.config) {
-      return {
-        type: 'message',
-        messageType: 'error',
-        content: t('Configuration not available.'),
-      };
-    }
-
     const trimmedArgs = args.trim();
 
     // If no arguments, show current language settings and usage
@@ -212,13 +287,15 @@ export const languageCommand: SlashCommand = {
       const currentUiLang = getCurrentLanguage();
       const currentLlmLang = getCurrentLlmOutputLanguage();
       const message = [
-        t('Current UI language: {{lang}}', { lang: currentUiLang }),
+        t('Current UI language: {{lang}}', {
+          lang: formatUiLanguageDisplay(currentUiLang as SupportedLanguage),
+        }),
         currentLlmLang
           ? t('Current LLM output language: {{lang}}', { lang: currentLlmLang })
           : t('LLM output language not set'),
         '',
         t('Available subcommands:'),
-        `  /language ui [zh-CN|en-US|ru-RU] - ${t('Set UI language')}`,
+        `  /language ui [${SUPPORTED_LANGUAGES.map((o) => o.id).join('|')}] - ${t('Set UI language')}`,
         `  /language output <language> - ${t('Set LLM output language')}`,
       ].join('\n');
 
@@ -229,115 +306,21 @@ export const languageCommand: SlashCommand = {
       };
     }
 
-    // Parse subcommand
-    const parts = trimmedArgs.split(/\s+/);
-    const subcommand = parts[0].toLowerCase();
-
-    if (subcommand === 'ui') {
-      // Handle /language ui [zh-CN|en-US|ru-RU]
-      if (parts.length === 1) {
-        // Show UI language subcommand help
-        return {
-          type: 'message',
-          messageType: 'info',
-          content: [
-            t('Set UI language'),
-            '',
-            t('Usage: /language ui [zh-CN|en-US|ru-RU]'),
-            '',
-            t('Available options:'),
-            t('  - zh-CN: Simplified Chinese'),
-            t('  - en-US: English'),
-            t('  - ru-RU: Russian'),
-            '',
-            t(
-              'To request additional UI language packs, please open an issue on GitHub.',
-            ),
-          ].join('\n'),
-        };
-      }
-
-      const langArg = parts[1].toLowerCase();
-      let targetLang: SupportedLanguage | null = null;
-
-      if (langArg === 'en' || langArg === 'english' || langArg === 'en-us') {
-        targetLang = 'en';
-      } else if (
-        langArg === 'zh' ||
-        langArg === 'chinese' ||
-        langArg === '中文' ||
-        langArg === 'zh-cn'
-      ) {
-        targetLang = 'zh';
-      } else if (
-        langArg === 'ru' ||
-        langArg === 'ru-RU' ||
-        langArg === 'russian' ||
-        langArg === 'русский'
-      ) {
-        targetLang = 'ru';
-      } else {
-        return {
-          type: 'message',
-          messageType: 'error',
-          content: t('Invalid language. Available: en-US, zh-CN, ru-RU'),
-        };
-      }
-
-      return setUiLanguage(context, targetLang);
-    } else if (subcommand === 'output') {
-      // Handle /language output <language>
-      if (parts.length === 1) {
-        return {
-          type: 'message',
-          messageType: 'info',
-          content: [
-            t('Set LLM output language'),
-            '',
-            t('Usage: /language output <language>'),
-            `  ${t('Example: /language output 中文')}`,
-          ].join('\n'),
-        };
-      }
-
-      // Join all parts after "output" as the language name
-      const language = parts.slice(1).join(' ');
-      return generateLlmOutputLanguageRuleFile(language);
-    } else {
-      // Backward compatibility: treat as UI language
-      const langArg = trimmedArgs.toLowerCase();
-      let targetLang: SupportedLanguage | null = null;
-
-      if (langArg === 'en' || langArg === 'english' || langArg === 'en-us') {
-        targetLang = 'en';
-      } else if (
-        langArg === 'zh' ||
-        langArg === 'chinese' ||
-        langArg === '中文' ||
-        langArg === 'zh-cn'
-      ) {
-        targetLang = 'zh';
-      } else if (
-        langArg === 'ru' ||
-        langArg === 'ru-RU' ||
-        langArg === 'russian' ||
-        langArg === 'русский'
-      ) {
-        targetLang = 'ru';
-      } else {
-        return {
-          type: 'message',
-          messageType: 'error',
-          content: [
-            t('Invalid command. Available subcommands:'),
-            '  - /language ui [zh-CN|en-US|ru-RU] - ' + t('Set UI language'),
-            '  - /language output <language> - ' + t('Set LLM output language'),
-          ].join('\n'),
-        };
-      }
-
+    // Handle backward compatibility for /language [lang]
+    const targetLang = parseUiLanguageArg(trimmedArgs);
+    if (targetLang) {
       return setUiLanguage(context, targetLang);
     }
+
+    return {
+      type: 'message',
+      messageType: 'error',
+      content: [
+        t('Invalid command. Available subcommands:'),
+        `  - /language ui [${SUPPORTED_LANGUAGES.map((o) => o.id).join('|')}] - ${t('Set UI language')}`,
+        '  - /language output <language> - ' + t('Set LLM output language'),
+      ].join('\n'),
+    };
   },
   subCommands: [
     {
@@ -358,11 +341,14 @@ export const languageCommand: SlashCommand = {
             content: [
               t('Set UI language'),
               '',
-              t('Usage: /language ui [zh-CN|en-US]'),
+              t('Usage: /language ui [{{options}}]', {
+                options: SUPPORTED_LANGUAGES.map((o) => o.id).join('|'),
+              }),
               '',
               t('Available options:'),
-              t('  - zh-CN: Simplified Chinese'),
-              t('  - en-US: English'),
+              ...SUPPORTED_LANGUAGES.map(
+                (o) => `  - ${o.id}: ${t(o.fullName)}`,
+              ),
               '',
               t(
                 'To request additional UI language packs, please open an issue on GitHub.',
@@ -371,99 +357,20 @@ export const languageCommand: SlashCommand = {
           };
         }
 
-        const langArg = trimmedArgs.toLowerCase();
-        let targetLang: SupportedLanguage | null = null;
-
-        if (langArg === 'en' || langArg === 'english' || langArg === 'en-us') {
-          targetLang = 'en';
-        } else if (
-          langArg === 'zh' ||
-          langArg === 'chinese' ||
-          langArg === '中文' ||
-          langArg === 'zh-cn'
-        ) {
-          targetLang = 'zh';
-        } else {
+        const targetLang = parseUiLanguageArg(trimmedArgs);
+        if (!targetLang) {
           return {
             type: 'message',
             messageType: 'error',
-            content: t('Invalid language. Available: en-US, zh-CN'),
+            content: t('Invalid language. Available: {{options}}', {
+              options: SUPPORTED_LANGUAGES.map((o) => o.id).join(','),
+            }),
           };
         }
 
         return setUiLanguage(context, targetLang);
       },
-      subCommands: [
-        {
-          name: 'zh-CN',
-          altNames: ['zh', 'chinese', '中文'],
-          get description() {
-            return t('Set UI language to Simplified Chinese (zh-CN)');
-          },
-          kind: CommandKind.BUILT_IN,
-          action: async (
-            context: CommandContext,
-            args: string,
-          ): Promise<MessageActionReturn> => {
-            if (args.trim().length > 0) {
-              return {
-                type: 'message',
-                messageType: 'error',
-                content: t(
-                  'Language subcommands do not accept additional arguments.',
-                ),
-              };
-            }
-            return setUiLanguage(context, 'zh');
-          },
-        },
-        {
-          name: 'en-US',
-          altNames: ['en', 'english'],
-          get description() {
-            return t('Set UI language to English (en-US)');
-          },
-          kind: CommandKind.BUILT_IN,
-          action: async (
-            context: CommandContext,
-            args: string,
-          ): Promise<MessageActionReturn> => {
-            if (args.trim().length > 0) {
-              return {
-                type: 'message',
-                messageType: 'error',
-                content: t(
-                  'Language subcommands do not accept additional arguments.',
-                ),
-              };
-            }
-            return setUiLanguage(context, 'en');
-          },
-        },
-        {
-          name: 'ru-RU',
-          altNames: ['ru', 'russian', 'русский'],
-          get description() {
-            return t('Set UI language to Russian (ru-RU)');
-          },
-          kind: CommandKind.BUILT_IN,
-          action: async (
-            context: CommandContext,
-            args: string,
-          ): Promise<MessageActionReturn> => {
-            if (args.trim().length > 0) {
-              return {
-                type: 'message',
-                messageType: 'error',
-                content: t(
-                  'Language subcommands do not accept additional arguments.',
-                ),
-              };
-            }
-            return setUiLanguage(context, 'ru');
-          },
-        },
-      ],
+      subCommands: SUPPORTED_LANGUAGES.map(createUiLanguageSubCommand),
     },
     {
       name: 'output',
@@ -496,3 +403,28 @@ export const languageCommand: SlashCommand = {
     },
   ],
 };
+
+/**
+ * Helper to create a UI language subcommand.
+ */
+function createUiLanguageSubCommand(option: LanguageDefinition): SlashCommand {
+  return {
+    name: option.id,
+    get description() {
+      return t('Set UI language to {{name}}', { name: option.fullName });
+    },
+    kind: CommandKind.BUILT_IN,
+    action: async (context, args) => {
+      if (args.trim().length > 0) {
+        return {
+          type: 'message',
+          messageType: 'error',
+          content: t(
+            'Language subcommands do not accept additional arguments.',
+          ),
+        };
+      }
+      return setUiLanguage(context, option.code);
+    },
+  };
+}

packages/sdk-typescript/src/utils/cliPath.ts

@@ -150,49 +150,48 @@ export function parseExecutableSpec(executableSpec?: string): {
   }
 
   // Check for runtime prefix (e.g., 'bun:/path/to/cli.js')
-  // Use whitelist mechanism: only treat as runtime spec if prefix matches supported runtimes
-  const supportedRuntimes = ['node', 'bun', 'tsx', 'deno'];
   const runtimeMatch = executableSpec.match(/^([^:]+):(.+)$/);
-
   if (runtimeMatch) {
     const [, runtime, filePath] = runtimeMatch;
-
-    // Only process as runtime specification if it matches a supported runtime
-    if (runtime && supportedRuntimes.includes(runtime)) {
-      if (!filePath) {
-        throw new Error(`Invalid runtime specification: '${executableSpec}'`);
-      }
-
-      if (!validateRuntimeAvailability(runtime)) {
-        throw new Error(
-          `Runtime '${runtime}' is not available on this system. Please install it first.`,
-        );
-      }
-
-      const resolvedPath = path.resolve(filePath);
-
-      if (!fs.existsSync(resolvedPath)) {
-        throw new Error(
-          `Executable file not found at '${resolvedPath}' for runtime '${runtime}'. ` +
-            'Please check the file path and ensure the file exists.',
-        );
-      }
-
-      if (!validateFileExtensionForRuntime(resolvedPath, runtime)) {
-        const ext = path.extname(resolvedPath);
-        throw new Error(
-          `File extension '${ext}' is not compatible with runtime '${runtime}'. ` +
-            `Expected extensions for ${runtime}: ${getExpectedExtensions(runtime).join(', ')}`,
-        );
-      }
-
-      return {
-        runtime,
-        executablePath: resolvedPath,
-        isExplicitRuntime: true,
-      };
+    if (!runtime || !filePath) {
+      throw new Error(`Invalid runtime specification: '${executableSpec}'`);
     }
-    // If not a supported runtime, fall through to treat as file path (e.g., Windows paths like 'D:\path\to\cli.js')
+
+    const supportedRuntimes = ['node', 'bun', 'tsx', 'deno'];
+    if (!supportedRuntimes.includes(runtime)) {
+      throw new Error(
+        `Unsupported runtime '${runtime}'. Supported runtimes: ${supportedRuntimes.join(', ')}`,
+      );
+    }
+
+    if (!validateRuntimeAvailability(runtime)) {
+      throw new Error(
+        `Runtime '${runtime}' is not available on this system. Please install it first.`,
+      );
+    }
+
+    const resolvedPath = path.resolve(filePath);
+
+    if (!fs.existsSync(resolvedPath)) {
+      throw new Error(
+        `Executable file not found at '${resolvedPath}' for runtime '${runtime}'. ` +
+          'Please check the file path and ensure the file exists.',
+      );
+    }
+
+    if (!validateFileExtensionForRuntime(resolvedPath, runtime)) {
+      const ext = path.extname(resolvedPath);
+      throw new Error(
+        `File extension '${ext}' is not compatible with runtime '${runtime}'. ` +
+          `Expected extensions for ${runtime}: ${getExpectedExtensions(runtime).join(', ')}`,
+      );
+    }
+
+    return {
+      runtime,
+      executablePath: resolvedPath,
+      isExplicitRuntime: true,
+    };
   }
 
   // Check if it's a command name (no path separators) or a file path

packages/sdk-typescript/test/unit/cliPath.test.ts

@@ -125,43 +125,12 @@ describe('CLI Path Utilities', () => {
         });
       });
 
-      it('should treat non-whitelisted runtime prefixes as command names', () => {
-        // With whitelist approach, 'invalid:format' is not recognized as a runtime spec
-        // so it's treated as a command name, which fails validation due to the colon
+      it('should throw for invalid runtime prefix format', () => {
         expect(() => parseExecutableSpec('invalid:format')).toThrow(
-          'Invalid command name',
+          'Unsupported runtime',
         );
       });
 
-      it('should treat Windows drive letters as file paths, not runtime specs', () => {
-        mockFs.existsSync.mockReturnValue(true);
-
-        // Test various Windows drive letters
-        const windowsPaths = [
-          'C:\\path\\to\\cli.js',
-          'D:\\path\\to\\cli.js',
-          'E:\\Users\\dev\\qwen\\cli.js',
-        ];
-
-        for (const winPath of windowsPaths) {
-          const result = parseExecutableSpec(winPath);
-
-          expect(result.isExplicitRuntime).toBe(false);
-          expect(result.runtime).toBeUndefined();
-          expect(result.executablePath).toBe(path.resolve(winPath));
-        }
-      });
-
-      it('should handle Windows paths with forward slashes', () => {
-        mockFs.existsSync.mockReturnValue(true);
-
-        const result = parseExecutableSpec('C:/path/to/cli.js');
-
-        expect(result.isExplicitRuntime).toBe(false);
-        expect(result.runtime).toBeUndefined();
-        expect(result.executablePath).toBe(path.resolve('C:/path/to/cli.js'));
-      });
-
       it('should throw when runtime-prefixed file does not exist', () => {
         mockFs.existsSync.mockReturnValue(false);
 
@@ -484,41 +453,6 @@ describe('CLI Path Utilities', () => {
         originalInput: `bun:${bundlePath}`,
       });
     });
-
-    it('should handle Windows paths with drive letters', () => {
-      const windowsPath = 'D:\\path\\to\\cli.js';
-      const result = prepareSpawnInfo(windowsPath);
-
-      expect(result).toEqual({
-        command: process.execPath,
-        args: [path.resolve(windowsPath)],
-        type: 'node',
-        originalInput: windowsPath,
-      });
-    });
-
-    it('should handle Windows paths with TypeScript files', () => {
-      const windowsPath = 'C:\\Users\\dev\\qwen\\index.ts';
-      const result = prepareSpawnInfo(windowsPath);
-
-      expect(result).toEqual({
-        command: 'tsx',
-        args: [path.resolve(windowsPath)],
-        type: 'tsx',
-        originalInput: windowsPath,
-      });
-    });
-
-    it('should not confuse Windows drive letters with runtime prefixes', () => {
-      // Ensure 'D:' is not treated as a runtime specification
-      const windowsPath = 'D:\\workspace\\project\\cli.js';
-      const result = prepareSpawnInfo(windowsPath);
-
-      // Should use node runtime based on .js extension, not treat 'D' as runtime
-      expect(result.type).toBe('node');
-      expect(result.command).toBe(process.execPath);
-      expect(result.args).toEqual([path.resolve(windowsPath)]);
-    });
   });
 
   describe('error cases', () => {
@@ -538,39 +472,21 @@ describe('CLI Path Utilities', () => {
       );
     });
 
-    it('should treat non-whitelisted runtime prefixes as command names', () => {
-      // With whitelist approach, 'invalid:spec' is not recognized as a runtime spec
-      // so it's treated as a command name, which fails validation due to the colon
+    it('should provide helpful error for invalid runtime specification', () => {
       expect(() => prepareSpawnInfo('invalid:spec')).toThrow(
-        'Invalid command name',
-      );
-    });
-
-    it('should handle Windows paths correctly even when file is missing', () => {
-      mockFs.existsSync.mockReturnValue(false);
-
-      expect(() => prepareSpawnInfo('D:\\missing\\cli.js')).toThrow(
-        'Executable file not found at',
-      );
-      // Should not throw 'Invalid command name' error (which would happen if 'D:' was treated as invalid command)
-      expect(() => prepareSpawnInfo('D:\\missing\\cli.js')).not.toThrow(
-        'Invalid command name',
+        'Unsupported runtime',
       );
     });
   });
 
   describe('comprehensive validation', () => {
     describe('runtime validation', () => {
-      it('should treat unsupported runtime prefixes as file paths', () => {
-        mockFs.existsSync.mockReturnValue(true);
-
-        // With whitelist approach, 'unsupported:' is not recognized as a runtime spec
-        // so 'unsupported:/path/to/file.js' is treated as a file path
-        const result = parseExecutableSpec('unsupported:/path/to/file.js');
-
-        // Should be treated as a file path, not a runtime specification
-        expect(result.isExplicitRuntime).toBe(false);
-        expect(result.runtime).toBeUndefined();
+      it('should reject unsupported runtimes', () => {
+        expect(() =>
+          parseExecutableSpec('unsupported:/path/to/file.js'),
+        ).toThrow(
+          "Unsupported runtime 'unsupported'. Supported runtimes: node, bun, tsx, deno",
+        );
       });
 
       it('should validate runtime availability for explicit runtime specs', () => {