feat: add language slash command

packages/cli/src/config/config.ts

@@ -24,6 +24,7 @@ import {
   WriteFileTool,
   resolveTelemetrySettings,
   FatalConfigError,
+  Storage,
 } from '@qwen-code/qwen-code-core';
 import type { Settings } from './settings.js';
 import yargs, { type Argv } from 'yargs';
@@ -560,6 +561,20 @@ export async function loadCliConfig(
     (e) => e.contextFiles,
   );
 
+  // Automatically load output-language.md if it exists
+  const outputLanguageFilePath = path.join(
+    Storage.getGlobalQwenDir(),
+    'output-language.md',
+  );
+  if (fs.existsSync(outputLanguageFilePath)) {
+    extensionContextFilePaths.push(outputLanguageFilePath);
+    if (debugMode) {
+      logger.debug(
+        `Found output-language.md, adding to context files: ${outputLanguageFilePath}`,
+      );
+    }
+  }
+
   const fileService = new FileDiscoveryService(cwd);
 
   const fileFiltering = {

packages/cli/src/i18n/locales/en.js

@@ -126,11 +126,11 @@ export default {
   'LLM output language not set': 'LLM output language not set',
   'Set UI language': 'Set UI language',
   'Set LLM output language': 'Set LLM output language',
-  'Usage: /lang ui [zh-CN|en-US]': 'Usage: /lang ui [zh-CN|en-US]',
-  'Usage: /lang output <language>': 'Usage: /lang output <language>',
-  'Example: /lang output 中文': 'Example: /lang output 中文',
-  'Example: /lang output English': 'Example: /lang output English',
-  'Example: /lang output 日本語': 'Example: /lang output 日本語',
+  'Usage: /language ui [zh-CN|en-US]': 'Usage: /language ui [zh-CN|en-US]',
+  'Usage: /language output <language>': 'Usage: /language output <language>',
+  'Example: /language output 中文': 'Example: /language output 中文',
+  'Example: /language output English': 'Example: /language output English',
+  'Example: /language output 日本語': 'Example: /language output 日本語',
   'UI language changed to {{lang}}': 'UI language changed to {{lang}}',
   'LLM output language rule file generated at {{path}}':
     'LLM output language rule file generated at {{path}}',

packages/cli/src/i18n/locales/zh.js

@@ -119,11 +119,11 @@ export default {
   'LLM output language not set': '未设置 LLM 输出语言',
   'Set UI language': '设置 UI 语言',
   'Set LLM output language': '设置 LLM 输出语言',
-  'Usage: /lang ui [zh-CN|en-US]': '用法：/lang ui [zh-CN|en-US]',
-  'Usage: /lang output <language>': '用法：/lang output <语言>',
-  'Example: /lang output 中文': '示例：/lang output 中文',
-  'Example: /lang output English': '示例：/lang output English',
-  'Example: /lang output 日本語': '示例：/lang output 日本語',
+  'Usage: /language ui [zh-CN|en-US]': '用法：/language ui [zh-CN|en-US]',
+  'Usage: /language output <language>': '用法：/language output <语言>',
+  'Example: /language output 中文': '示例：/language output 中文',
+  'Example: /language output English': '示例：/language output English',
+  'Example: /language output 日本語': '示例：/language output 日本語',
   'UI language changed to {{lang}}': 'UI 语言已更改为 {{lang}}',
   'LLM output language rule file generated at {{path}}':
     'LLM 输出语言规则文件已生成于 {{path}}',

packages/cli/src/services/BuiltinCommandLoader.ts

@@ -24,6 +24,7 @@ import { extensionsCommand } from '../ui/commands/extensionsCommand.js';
 import { helpCommand } from '../ui/commands/helpCommand.js';
 import { ideCommand } from '../ui/commands/ideCommand.js';
 import { initCommand } from '../ui/commands/initCommand.js';
+import { languageCommand } from '../ui/commands/languageCommand.js';
 import { mcpCommand } from '../ui/commands/mcpCommand.js';
 import { memoryCommand } from '../ui/commands/memoryCommand.js';
 import { modelCommand } from '../ui/commands/modelCommand.js';
@@ -72,6 +73,7 @@ export class BuiltinCommandLoader implements ICommandLoader {
       helpCommand,
       await ideCommand(),
       initCommand,
+      languageCommand,
       mcpCommand,
       memoryCommand,
       modelCommand,

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

@@ -0,0 +1,435 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type {
+  SlashCommand,
+  CommandContext,
+  SlashCommandActionReturn,
+  MessageActionReturn,
+} from './types.js';
+import { CommandKind } from './types.js';
+import { SettingScope } from '../../config/settings.js';
+import {
+  setLanguageAsync,
+  getCurrentLanguage,
+  type SupportedLanguage,
+  t,
+} from '../../i18n/index.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';
+
+/**
+ * Generates the LLM output language rule template based on the language name.
+ */
+function generateLlmOutputLanguageRule(language: string): string {
+  return `# ${language} Response Rules
+
+## Core Rules
+
+**ALL OUTPUTS MUST USE ${language.toUpperCase()}, WITHOUT EXCEPTION.** This includes: conversation replies, tool call results, generated files, documentation, comments, and error messages. Even if the user asks in English, you MUST respond in ${language}.
+
+## Tool Call Outputs
+
+All tool execution result descriptions, success/failure messages, and summary explanations must use ${language}:
+
+- File operations: \`read_file\`, \`write_file\`, \`edit_file\`, etc.
+- Code search: \`codebase_search\`, \`grep\`, etc.
+- Terminal commands: \`run_terminal_cmd\` execution result descriptions
+- Other tools: \`todo_write\`, \`web_search\`, etc.
+
+**Examples:**
+
+- ✅ "Successfully read file config.json, contains 15 lines" (translated to ${language})
+- ❌ "Successfully read file config.json, contains 15 lines" (in English when ${language} is required)
+
+**Note:** Variable names and function names in code can remain in English, but comments, documentation, and all explanatory text must be in ${language}.
+`;
+}
+
+/**
+ * Gets the path to the LLM output language rule file.
+ */
+function getLlmOutputLanguageRulePath(): string {
+  return path.join(
+    Storage.getGlobalQwenDir(),
+    LLM_OUTPUT_LANGUAGE_RULE_FILENAME,
+  );
+}
+
+/**
+ * Gets the current LLM output language from the rule file if it exists.
+ */
+function getCurrentLlmOutputLanguage(): string | null {
+  const filePath = getLlmOutputLanguageRulePath();
+  if (fs.existsSync(filePath)) {
+    try {
+      const content = fs.readFileSync(filePath, 'utf-8');
+      // Extract language name from the first line (e.g., "# Chinese Response Rules" -> "Chinese")
+      const match = content.match(/^#\s+(.+?)\s+Response Rules/i);
+      if (match) {
+        return match[1];
+      }
+    } catch {
+      // Ignore errors
+    }
+  }
+  return null;
+}
+
+/**
+ * Sets the UI language and persists it to settings.
+ */
+async function setUiLanguage(
+  context: CommandContext,
+  lang: SupportedLanguage,
+): Promise<MessageActionReturn> {
+  const { services } = context;
+  const { settings } = services;
+
+  if (!services.config) {
+    return {
+      type: 'message',
+      messageType: 'error',
+      content: t('Configuration not available.'),
+    };
+  }
+
+  // Set language in i18n system (async to support JS translation files)
+  await setLanguageAsync(lang);
+
+  // Persist to settings (user scope)
+  if (settings && typeof settings.setValue === 'function') {
+    try {
+      settings.setValue(SettingScope.User, 'general.language', lang);
+    } catch (error) {
+      console.warn('Failed to save language setting:', error);
+    }
+  }
+
+  // Reload commands to update their descriptions with the new language
+  context.ui.reloadCommands();
+
+  return {
+    type: 'message',
+    messageType: 'info',
+    content: t('UI language changed to {{lang}}', { lang }),
+  };
+}
+
+/**
+ * Generates the LLM output language rule file.
+ */
+function generateLlmOutputLanguageRuleFile(
+  language: string,
+): Promise<MessageActionReturn> {
+  try {
+    const filePath = getLlmOutputLanguageRulePath();
+    const content = generateLlmOutputLanguageRule(language);
+
+    // Ensure directory exists
+    const dir = path.dirname(filePath);
+    fs.mkdirSync(dir, { recursive: true });
+
+    // Write file (overwrite if exists)
+    fs.writeFileSync(filePath, content, 'utf-8');
+
+    return Promise.resolve({
+      type: 'message',
+      messageType: 'info',
+      content: t('LLM output language rule file generated at {{path}}', {
+        path: filePath,
+      }),
+    });
+  } catch (error) {
+    return Promise.resolve({
+      type: 'message',
+      messageType: 'error',
+      content: t(
+        'Failed to generate LLM output language rule file: {{error}}',
+        {
+          error: error instanceof Error ? error.message : String(error),
+        },
+      ),
+    });
+  }
+}
+
+export const languageCommand: SlashCommand = {
+  name: 'language',
+  get description() {
+    return t('View or change the language setting');
+  },
+  kind: CommandKind.BUILT_IN,
+  action: async (
+    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
+    if (!trimmedArgs) {
+      const currentUiLang = getCurrentLanguage();
+      const currentLlmLang = getCurrentLlmOutputLanguage();
+      const message = [
+        t('Current UI language: {{lang}}', { lang: currentUiLang }),
+        currentLlmLang
+          ? t('Current LLM output language: {{lang}}', { lang: currentLlmLang })
+          : t('LLM output language not set'),
+        '',
+        t('Available subcommands:'),
+        `  /language ui [zh-CN|en-US] - ${t('Set UI language')}`,
+        `  /language output <language> - ${t('Set LLM output language')}`,
+      ].join('\n');
+
+      return {
+        type: 'message',
+        messageType: 'info',
+        content: message,
+      };
+    }
+
+    // Parse subcommand
+    const parts = trimmedArgs.split(/\s+/);
+    const subcommand = parts[0].toLowerCase();
+
+    if (subcommand === 'ui') {
+      // Handle /language ui [zh-CN|en-US]
+      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]'),
+            '',
+            t('Available options:'),
+            t('  - zh-CN: Simplified Chinese'),
+            t('  - en-US: English'),
+            '',
+            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 {
+        return {
+          type: 'message',
+          messageType: 'error',
+          content: t('Invalid language. Available: en-US, zh-CN'),
+        };
+      }
+
+      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 {
+        return {
+          type: 'message',
+          messageType: 'error',
+          content: [
+            t('Invalid command. Available subcommands:'),
+            '  - /language ui [zh-CN|en-US] - ' + t('Set UI language'),
+            '  - /language output <language> - ' + t('Set LLM output language'),
+          ].join('\n'),
+        };
+      }
+
+      return setUiLanguage(context, targetLang);
+    }
+  },
+  subCommands: [
+    {
+      name: 'ui',
+      get description() {
+        return t('Set UI language');
+      },
+      kind: CommandKind.BUILT_IN,
+      action: async (
+        context: CommandContext,
+        args: string,
+      ): Promise<MessageActionReturn> => {
+        const trimmedArgs = args.trim();
+        if (!trimmedArgs) {
+          return {
+            type: 'message',
+            messageType: 'info',
+            content: [
+              t('Set UI language'),
+              '',
+              t('Usage: /language ui [zh-CN|en-US]'),
+              '',
+              t('Available options:'),
+              t('  - zh-CN: Simplified Chinese'),
+              t('  - en-US: English'),
+              '',
+              t(
+                'To request additional UI language packs, please open an issue on GitHub.',
+              ),
+            ].join('\n'),
+          };
+        }
+
+        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 {
+          return {
+            type: 'message',
+            messageType: 'error',
+            content: t('Invalid language. Available: en-US, zh-CN'),
+          };
+        }
+
+        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: 'output',
+      get description() {
+        return t('Set LLM output language');
+      },
+      kind: CommandKind.BUILT_IN,
+      action: async (
+        context: CommandContext,
+        args: string,
+      ): Promise<MessageActionReturn> => {
+        const trimmedArgs = args.trim();
+        if (!trimmedArgs) {
+          return {
+            type: 'message',
+            messageType: 'info',
+            content: [
+              t('Set LLM output language'),
+              '',
+              t('Usage: /language output <language>'),
+              `  ${t('Example: /language output 中文')}`,
+              `  ${t('Example: /language output English')}`,
+              `  ${t('Example: /language output 日本語')}`,
+            ].join('\n'),
+          };
+        }
+
+        return generateLlmOutputLanguageRuleFile(trimmedArgs);
+      },
+    },
+  ],
+};