diff --git a/site/index.html b/site/index.html
index fc4d54b9..f81811ad 100644
--- a/site/index.html
+++ b/site/index.html
@@ -16,6 +16,29 @@
     <meta property="og:image" content="https://cchaha.ai/images/banner.png">
     <meta name="twitter:card" content="summary_large_image">
     <title>Claude Code Haha — Claude Code 的本地优先桌面客户端</title>
+    <script>
+      // 首帧就把语言定下来：中文浏览器留在中文站，其余跳英文站。等 React 起来再跳的话，
+      // 英文用户会先看到一整屏中文。只认根路径，带语言前缀的地址是用户的明确意图。
+      // 判定规则与 src/lib/locale.js 是同一套，check-docs.mjs 盯着两处不漂移。
+      (function () {
+        try {
+          if (window.location.pathname.replace(/\/+$/, '') !== '') return
+
+          var stored = localStorage.getItem('cch-locale')
+          var locale = stored === 'en' || stored === 'zh'
+            ? stored
+            : ((navigator.languages || [navigator.language || '']).some(function (tag) {
+              return /^zh(?:-|$)/i.test(String(tag).trim())
+            }) ? 'zh' : 'en')
+
+          if (locale === 'en') {
+            window.location.replace('/en' + window.location.search + window.location.hash)
+          }
+        } catch (error) {
+          // 读不到偏好就维持中文站，别让语言分流把首页整个拦死。
+        }
+      })()
+    </script>
     <script>
       // 首帧就把主题定下来，避免深色偏好的用户先闪一下白屏。
       (function () {
diff --git a/site/package.json b/site/package.json
index 2fbd96a4..dbdace81 100644
--- a/site/package.json
+++ b/site/package.json
@@ -11,7 +11,8 @@
     "postbuild": "node scripts/prepare-static-output.mjs",
     "preview": "vite preview --host 0.0.0.0",
     "check:docs": "node scripts/check-docs.mjs",
-    "check": "npm run check:docs"
+    "test": "node --test \"src/**/*.test.js\"",
+    "check": "npm run check:docs && npm test"
   },
   "dependencies": {
     "dompurify": "^3.3.0",
diff --git a/site/scripts/check-docs.mjs b/site/scripts/check-docs.mjs
index 1ad01382..b05f3c1b 100644
--- a/site/scripts/check-docs.mjs
+++ b/site/scripts/check-docs.mjs
@@ -46,6 +46,40 @@ function isImageTarget(target) {
   return /\.(?:avif|gif|jpe?g|png|svg|webp)$/i.test(withoutSuffix(target))
 }
 
+/**
+ * 语言分流的判定规则在两处各有一份：src/lib/locale.js（可测的模块）和 index.html 里的内联
+ * 副本（首帧就要跳，等不到模块加载）。两处漂移不会报错，只会让首页悄悄按旧规则分流，所以
+ * 在这里钉死：storage key 和中文判定正则必须逐字一致，且内联脚本必须只在根路径动手。
+ */
+async function checkLocaleRedirect() {
+  const problems = []
+  const moduleSource = await fs.readFile(path.join(paths.siteDir, 'src/lib/locale.js'), 'utf8')
+  const shellSource = await fs.readFile(path.join(paths.siteDir, 'index.html'), 'utf8')
+
+  const storageKey = moduleSource.match(/LOCALE_STORAGE_KEY\s*=\s*'([^']+)'/)?.[1]
+  const chineseTag = moduleSource.match(/const CHINESE_TAG\s*=\s*(\/.+\/i)/)?.[1]
+
+  if (!storageKey || !chineseTag) {
+    problems.push('src/lib/locale.js: 读不出 LOCALE_STORAGE_KEY 或 CHINESE_TAG，防漂移校验失效')
+    return problems
+  }
+
+  if (!shellSource.includes(`localStorage.getItem('${storageKey}')`)) {
+    problems.push(`index.html: 内联语言脚本没有用 '${storageKey}'，与 src/lib/locale.js 不一致`)
+  }
+
+  if (!shellSource.includes(chineseTag)) {
+    problems.push(`index.html: 内联语言脚本的中文判定与 src/lib/locale.js 的 ${chineseTag} 不一致`)
+  }
+
+  // 少了这道判断，/en/start 这类地址也会被卷进分流。
+  if (!shellSource.includes("window.location.pathname.replace(/\\/+$/, '') !== ''")) {
+    problems.push('index.html: 内联语言脚本缺少「只在根路径生效」的判断')
+  }
+
+  return problems
+}
+
 async function main() {
   const { records } = await generateDocsManifest()
   const routes = new Set([
@@ -55,7 +89,7 @@ async function main() {
     '/en/docs',
     ...records.map((record) => record.path),
   ])
-  const problems = []
+  const problems = [...await checkLocaleRedirect()]
   let checkedTargets = 0
 
   for (const record of records) {
diff --git a/site/src/components/SiteHeader.jsx b/site/src/components/SiteHeader.jsx
index a0c15aa3..452f7913 100644
--- a/site/src/components/SiteHeader.jsx
+++ b/site/src/components/SiteHeader.jsx
@@ -1,6 +1,7 @@
 import { useEffect, useState } from 'react'
 import Icon from './icons'
 import { toSiteHref } from '../content/docs'
+import { rememberLocale } from '../lib/locale'
 import { useTheme } from '../lib/theme'
 import SearchDialog from './SearchDialog'
 
@@ -83,7 +84,16 @@ export default function SiteHeader({ activeSection, locale = 'zh', localeHref })
                 {label}
               </a>
             ))}
-            <a href={toSiteHref(switchHref)} onClick={() => setOpen(false)}>{c.toEnglish}</a>
+            <a
+              href={toSiteHref(switchHref)}
+              onClick={() => {
+                // 手动切过就记住，别让下次进首页时又被浏览器语言盖回去。
+                rememberLocale(locale === 'en' ? 'zh' : 'en')
+                setOpen(false)
+              }}
+            >
+              {c.toEnglish}
+            </a>
           </nav>
 
           <div className="header-tools">
diff --git a/site/src/lib/locale.js b/site/src/lib/locale.js
new file mode 100644
index 00000000..4e2cfdb0
--- /dev/null
+++ b/site/src/lib/locale.js
@@ -0,0 +1,48 @@
+/**
+ * 站点语言分流。
+ *
+ * 只有根路径 `/` 会按浏览器语言自动选：中文浏览器留在中文站，其余跳 `/en`。
+ * 带语言前缀的地址（`/en`、`/start`、`/en/start`）都是用户点进来的明确意图，一概不动 ——
+ * 否则英文用户点一条中文文档链接会被莫名踢走。
+ *
+ * 手动切过语言之后，选择记进 localStorage，之后回到 `/` 就按记住的来，不再被浏览器语言
+ * 盖掉；不然导航里的切换器等于没用：浏览器是中文的人切到英文，下次进首页又被弹回中文。
+ *
+ * 注意：同一套判断在 index.html 里有一份内联副本 —— 首帧就得跳完，等不到这个模块加载。
+ * 改 STORAGE_KEY 或判定规则时两处要一起改，check-docs.mjs 会盯着它们不漂移。
+ */
+
+export const LOCALE_STORAGE_KEY = 'cch-locale'
+
+/** BCP-47 里中文一律是 zh / zh-CN / zh-TW / zh-Hans…，但 zhuang 之类不算。 */
+const CHINESE_TAG = /^zh(?:-|$)/i
+
+export function prefersChinese(languages) {
+  if (!Array.isArray(languages)) return false
+  return languages.some((tag) => typeof tag === 'string' && CHINESE_TAG.test(tag.trim()))
+}
+
+export function normalizeStoredLocale(value) {
+  return value === 'en' || value === 'zh' ? value : null
+}
+
+/**
+ * 根路径该跳去哪；返回 null 表示留在原地（中文站）。
+ */
+export function resolveRootRedirect({ languages, pathname, stored }) {
+  if (String(pathname ?? '/').replace(/\/+$/, '') !== '') return null
+
+  const locale = normalizeStoredLocale(stored) || (prefersChinese(languages) ? 'zh' : 'en')
+  return locale === 'en' ? '/en' : null
+}
+
+export function rememberLocale(locale) {
+  const value = normalizeStoredLocale(locale)
+  if (!value) return
+
+  try {
+    localStorage.setItem(LOCALE_STORAGE_KEY, value)
+  } catch {
+    // 隐私模式下 localStorage 直接抛，记不住偏好也不能让语言切换本身失败。
+  }
+}
diff --git a/site/src/lib/locale.test.js b/site/src/lib/locale.test.js
new file mode 100644
index 00000000..94481aab
--- /dev/null
+++ b/site/src/lib/locale.test.js
@@ -0,0 +1,82 @@
+import assert from 'node:assert/strict'
+import { describe, it } from 'node:test'
+
+import { normalizeStoredLocale, prefersChinese, resolveRootRedirect } from './locale.js'
+
+describe('prefersChinese', () => {
+  it('认所有中文变体', () => {
+    for (const tag of ['zh', 'zh-CN', 'zh-TW', 'zh-HK', 'zh-Hans', 'zh-Hant-TW', 'ZH-cn']) {
+      assert.equal(prefersChinese([tag]), true, tag)
+    }
+  })
+
+  it('不把 zh 开头的其他语言当中文', () => {
+    // zhuang（壮语）真实存在于 BCP-47，前缀匹配写松了会误判。
+    assert.equal(prefersChinese(['zha']), false)
+    assert.equal(prefersChinese(['zhuang']), false)
+  })
+
+  it('列表里任意一项是中文就算中文', () => {
+    assert.equal(prefersChinese(['en-US', 'zh-CN']), true)
+    assert.equal(prefersChinese(['en-US', 'ja', 'ko']), false)
+  })
+
+  it('输入不是数组或含脏值时不炸', () => {
+    assert.equal(prefersChinese(undefined), false)
+    assert.equal(prefersChinese(null), false)
+    assert.equal(prefersChinese([]), false)
+    assert.equal(prefersChinese([null, undefined, 42, ' zh-CN ']), true)
+  })
+})
+
+describe('normalizeStoredLocale', () => {
+  it('只接受 zh / en', () => {
+    assert.equal(normalizeStoredLocale('zh'), 'zh')
+    assert.equal(normalizeStoredLocale('en'), 'en')
+    assert.equal(normalizeStoredLocale('fr'), null)
+    assert.equal(normalizeStoredLocale(''), null)
+    assert.equal(normalizeStoredLocale(null), null)
+  })
+})
+
+describe('resolveRootRedirect', () => {
+  it('中文浏览器留在中文站', () => {
+    assert.equal(resolveRootRedirect({ languages: ['zh-CN'], pathname: '/' }), null)
+  })
+
+  it('非中文浏览器跳英文站', () => {
+    assert.equal(resolveRootRedirect({ languages: ['en-US'], pathname: '/' }), '/en')
+    assert.equal(resolveRootRedirect({ languages: ['ja-JP'], pathname: '/' }), '/en')
+  })
+
+  it('拿不到浏览器语言时按英文兜底', () => {
+    assert.equal(resolveRootRedirect({ languages: [], pathname: '/' }), '/en')
+    assert.equal(resolveRootRedirect({ pathname: '/' }), '/en')
+  })
+
+  it('根路径的尾斜杠和空串都算根', () => {
+    for (const pathname of ['/', '', '//']) {
+      assert.equal(resolveRootRedirect({ languages: ['en'], pathname }), '/en', JSON.stringify(pathname))
+    }
+  })
+
+  it('只动根路径，带前缀的地址一概不碰', () => {
+    // 这是整个功能的安全边界：英文用户点开中文文档不该被踢走，反之亦然。
+    const cases = ['/en', '/en/', '/start', '/en/start', '/desktop/pets', '/internals']
+    for (const pathname of cases) {
+      assert.equal(resolveRootRedirect({ languages: ['en-US'], pathname }), null, pathname)
+      assert.equal(resolveRootRedirect({ languages: ['zh-CN'], pathname }), null, pathname)
+    }
+  })
+
+  it('记住的偏好优先于浏览器语言', () => {
+    // 中文浏览器手动切到英文后，回首页不该被弹回中文，否则切换器等于没用。
+    assert.equal(resolveRootRedirect({ languages: ['zh-CN'], pathname: '/', stored: 'en' }), '/en')
+    assert.equal(resolveRootRedirect({ languages: ['en-US'], pathname: '/', stored: 'zh' }), null)
+  })
+
+  it('偏好是脏值时退回浏览器语言', () => {
+    assert.equal(resolveRootRedirect({ languages: ['zh-CN'], pathname: '/', stored: 'garbage' }), null)
+    assert.equal(resolveRootRedirect({ languages: ['en-US'], pathname: '/', stored: '' }), '/en')
+  })
+})
diff --git a/site/src/pages/home/HomePage.jsx b/site/src/pages/home/HomePage.jsx
index b8b5861d..28d2502f 100644
--- a/site/src/pages/home/HomePage.jsx
+++ b/site/src/pages/home/HomePage.jsx
@@ -2,6 +2,7 @@ import { useEffect, useState } from 'react'
 import Icon from '../../components/icons'
 import SiteHeader, { DOWNLOAD_URL, GITHUB_URL } from '../../components/SiteHeader'
 import { toSiteHref } from '../../content/docs'
+import { rememberLocale } from '../../lib/locale'
 import { setPageMeta } from '../../lib/meta'
 import { content, mascotAccents, mascots } from './content'
 import './home.css'
@@ -278,7 +279,12 @@ function Footer({ c, locale }) {
           </nav>
         ))}
         <div className="site-footer__meta">
-          <a href={toSiteHref(locale === 'en' ? '/' : '/en')}>{locale === 'en' ? '中文' : 'English'}</a>
+          <a
+            href={toSiteHref(locale === 'en' ? '/' : '/en')}
+            onClick={() => rememberLocale(locale === 'en' ? 'zh' : 'en')}
+          >
+            {locale === 'en' ? '中文' : 'English'}
+          </a>
         </div>
       </div>
     </footer>