diff --git a/messages/en.json b/messages/en.json
index 1ec6b4191..64f9a461e 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -1757,9 +1757,9 @@
         "organizeAs": "Organize as",
         "template": "Template",
         "setting": "Settings",
-        "confirm": "确认",
-        "cancel": "取消",
-        "removeThinking": "移除思考过程",
+        "confirm": "Confirm",
+        "cancel": "Cancel",
+        "removeThinking": "Remove thinking process",
         "stop": "Stop"
       }
     },
@@ -1800,11 +1800,11 @@
         "noMatchingConversations": "No matching conversations found",
         "noConversationHistory": "No conversation history yet",
         "quickPrompts": {
-          "title": "快速开始",
-          "writeNote": "帮我写一篇笔记",
-          "summarize": "帮我总结这段内容",
-          "brainstorm": "帮我头脑风暴一些想法",
-          "explain": "帮我解释这个概念"
+          "title": "Quick Start",
+          "writeNote": "Help me write a note",
+          "summarize": "Help me summarize this content",
+          "brainstorm": "Help me brainstorm some ideas",
+          "explain": "Help me explain this concept"
         }
       },
       "newChat": "New Chat with New Tag",
diff --git a/package.json b/package.json
index 92a233ae3..402f63083 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,8 @@
     "build": "next build --turbopack",
     "start": "next start --turbopack -p 3456",
     "lint": "next lint",
+    "lint:i18n": "node scripts/check-i18n.js",
+    "audit:locales": "node scripts/audit-locales.js",
     "tauri": "tauri",
     "docs:build": "npm --prefix ./docs run build",
     "sync-version": "./scripts/sync-version.sh",
diff --git a/scripts/audit-locales.js b/scripts/audit-locales.js
new file mode 100644
index 000000000..d519b0ead
--- /dev/null
+++ b/scripts/audit-locales.js
@@ -0,0 +1,58 @@
+/**
+ * Verifies that every key in messages/zh.json exists in all other locale files.
+ * Exits with code 1 if any locale is missing keys.
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+const MESSAGES_DIR = path.join(__dirname, '..', 'messages');
+const LOCALES = ['en.json', 'ja.json', 'pt-BR.json', 'zh-TW.json'];
+
+function getAllKeys(obj, prefix = '') {
+  const keys = new Set();
+  for (const [k, v] of Object.entries(obj)) {
+    const full = prefix ? `${prefix}.${k}` : k;
+    if (typeof v === 'object' && v !== null && !Array.isArray(v)) {
+      for (const child of getAllKeys(v, full)) {
+        keys.add(child);
+      }
+    } else {
+      keys.add(full);
+    }
+  }
+  return keys;
+}
+
+const zh = JSON.parse(fs.readFileSync(path.join(MESSAGES_DIR, 'zh.json'), 'utf-8'));
+const zhKeys = getAllKeys(zh);
+
+let failed = false;
+for (const file of LOCALES) {
+  const fullPath = path.join(MESSAGES_DIR, file);
+  if (!fs.existsSync(fullPath)) {
+    console.error(`❌ Missing locale file: ${file}`);
+    failed = true;
+    continue;
+  }
+  const data = JSON.parse(fs.readFileSync(fullPath, 'utf-8'));
+  const keys = getAllKeys(data);
+  const missing = [];
+  for (const k of zhKeys) {
+    if (!keys.has(k)) {
+      missing.push(k);
+    }
+  }
+  if (missing.length > 0) {
+    console.error(`❌ ${file} missing ${missing.length} key(s):`);
+    missing.slice(0, 20).forEach((k) => console.error('   ' + k));
+    if (missing.length > 20) {
+      console.error(`   ... and ${missing.length - 20} more`);
+    }
+    failed = true;
+  } else {
+    console.log(`✅ ${file} has all ${zhKeys.size} keys`);
+  }
+}
+
+process.exit(failed ? 1 : 0);
diff --git a/scripts/check-i18n.js b/scripts/check-i18n.js
new file mode 100644
index 000000000..bb470f950
--- /dev/null
+++ b/scripts/check-i18n.js
@@ -0,0 +1,99 @@
+/**
+ * Regression guard: scans src/ for Chinese characters in UI-facing code.
+ * Exits with code 1 if new hardcoded Chinese strings are found.
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+const SRC_DIR = path.join(__dirname, '..', 'src');
+
+// Allow-list: strings that are intentionally Chinese (model names, comments, etc.)
+const ALLOWLIST = new Set([
+  '简体中文',
+  '日本語',
+]);
+
+// Extensions to scan
+const EXTENSIONS = new Set(['.ts', '.tsx', '.js', '.jsx']);
+
+function hasChinese(str) {
+  return /[\u4e00-\u9fff]/.test(str);
+}
+
+function extractStringLiterals(line) {
+  const strings = [];
+  const singleQuote = /'((?:[^'\\]|\\.)*)'/g;
+  const doubleQuote = /"((?:[^"\\]|\\.)*)"/g;
+  const backtick = /`((?:[^`\\]|\\.)*)`/g;
+  let m;
+  while ((m = singleQuote.exec(line)) !== null) strings.push(m[1]);
+  while ((m = doubleQuote.exec(line)) !== null) strings.push(m[1]);
+  while ((m = backtick.exec(line)) !== null) strings.push(m[1]);
+  return strings;
+}
+
+const violations = [];
+
+function scanFile(filePath) {
+  const content = fs.readFileSync(filePath, 'utf-8');
+  const lines = content.split('\n');
+  let inBlockComment = false;
+  lines.forEach((line, idx) => {
+    // Track block comment state
+    if (inBlockComment) {
+      if (line.includes('*/')) {
+        inBlockComment = false;
+      }
+      return;
+    }
+    if (line.includes('/*')) {
+      inBlockComment = !line.includes('*/');
+      if (inBlockComment) return;
+    }
+
+    // Skip import lines that load messages JSON (those contain locale codes, not UI)
+    if (line.includes('messages/') && line.includes('import')) return;
+    // Skip comment-only lines
+    if (line.trim().startsWith('//')) return;
+
+    const strings = extractStringLiterals(line);
+    for (const str of strings) {
+      if (!hasChinese(str)) continue;
+      if (ALLOWLIST.has(str)) continue;
+      violations.push(`${filePath}:${idx + 1}: ${str.slice(0, 60)}`);
+    }
+
+    // Also catch raw JSX text nodes (e.g. <span>保存</span>)
+    const jsxTextRegex = />\s*([^<]*[\u4e00-\u9fff][^<]*)\s*</g;
+    let jsxMatch;
+    while ((jsxMatch = jsxTextRegex.exec(line)) !== null) {
+      const text = jsxMatch[1].trim();
+      if (ALLOWLIST.has(text)) continue;
+      violations.push(`${filePath}:${idx + 1}: ${text.slice(0, 60)}`);
+    }
+  });
+}
+
+function walk(dir) {
+  for (const entry of fs.readdirSync(dir)) {
+    const full = path.join(dir, entry);
+    const stat = fs.statSync(full);
+    if (stat.isDirectory()) {
+      walk(full);
+    } else if (EXTENSIONS.has(path.extname(full))) {
+      scanFile(full);
+    }
+  }
+}
+
+walk(SRC_DIR);
+
+if (violations.length > 0) {
+  console.error(`❌ Found ${violations.length} hardcoded Chinese string(s):`);
+  violations.forEach((v) => console.error('   ' + v));
+  process.exit(1);
+} else {
+  console.log('✅ No hardcoded Chinese strings found in src/');
+  process.exit(0);
+}
diff --git a/src/lib/i18n.ts b/src/lib/i18n.ts
new file mode 100644
index 000000000..0b7baa1f2
--- /dev/null
+++ b/src/lib/i18n.ts
@@ -0,0 +1,65 @@
+/**
+ * Lightweight i18n helper for non-React modules (Zustand stores, sync utilities).
+ * Reads the active locale from localStorage (same key used by NextIntlProvider)
+ * and returns a synchronous t() function backed by the loaded messages.
+ *
+ * Messages are cached per locale to avoid repeated disk reads.
+ */
+
+const CACHE = new Map<string, Record<string, any>>();
+
+function getLocale(): string {
+  if (typeof localStorage !== 'undefined') {
+    return localStorage.getItem('app-language') || 'zh';
+  }
+  return 'zh';
+}
+
+function resolvePath(obj: any, path: string): string | undefined {
+  const parts = path.split('.');
+  let current = obj;
+  for (const part of parts) {
+    if (current == null || typeof current !== 'object') {
+      return undefined;
+    }
+    current = current[part];
+  }
+  return typeof current === 'string' ? current : undefined;
+}
+
+async function loadMessages(locale: string): Promise<Record<string, any>> {
+  if (CACHE.has(locale)) {
+    return CACHE.get(locale)!;
+  }
+  try {
+    const mod = await import(`../../messages/${locale}.json`);
+    const messages = mod.default || mod;
+    CACHE.set(locale, messages);
+    return messages;
+  } catch {
+    const fallback = await import(`../../messages/zh.json`);
+    const messages = fallback.default || fallback;
+    CACHE.set(locale, messages);
+    return messages;
+  }
+}
+
+export async function getI18n(): Promise<{ t: (key: string) => string }> {
+  const locale = getLocale();
+  const messages = await loadMessages(locale);
+  return {
+    t(key: string): string {
+      const value = resolvePath(messages, key);
+      if (typeof value === 'string') {
+        return value;
+      }
+      // fallback to zh if missing in target locale
+      const fallback = resolvePath(CACHE.get('zh') || messages, key);
+      return fallback ?? key;
+    },
+  };
+}
+
+export function clearI18nCache(): void {
+  CACHE.clear();
+}