feat: implement browser language detection and auto-redirect for homepage by Copilot · Pull Request #30 · objectstack-ai/framework

Copilot · 2026-01-19T14:29:24Z

The homepage now redirects users to their language-preferred interface based on browser Accept-Language headers. Chinese users are redirected to /cn, while English users remain on / (the default).

Changes

Custom Middleware (apps/docs/middleware.ts)

Replaced fumadocs default middleware with custom implementation
Maps Chinese language codes (zh, zh-CN, zh-TW, zh-HK) → cn
English (default): Internal rewrite to /en, URL stays /
Non-default languages: HTTP 307 redirect to localized path + cookie persistence
Cookie options: sameSite: 'lax', path: '/'

Dependencies (apps/docs/package.json)

Added negotiator for Accept-Language parsing
Added @types/negotiator

Implementation

function getPreferredLanguage(request: NextRequest): string {
  // Cookie first, then Accept-Language header
  const cookieLocale = request.cookies.get('FD_LOCALE')?.value;
  if (cookieLocale && SUPPORTED_LANGUAGES.includes(cookieLocale)) {
    return cookieLocale;
  }

  const negotiator = new Negotiator({ headers: Object.fromEntries(request.headers.entries()) });
  const browserLanguages = negotiator.languages().map(normalizeLanguage);
  
  return browserLanguages.find(lang => SUPPORTED_LANGUAGES.includes(lang)) 
    || i18n.defaultLanguage;
}

Behavior

Browser Language	URL Visited	Result
`en-US`	`/`	Stays on `/` (rewritten to `/en` internally)
`zh-CN`	`/`	Redirects to `/cn`
Any	`/en`	Redirects to `/` (strips default locale)

Screenshots

English Homepage (/)

Chinese Homepage (/cn)

Original prompt

首页应根据当前的语言自动跳转到对应的语言界面

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

vercel · 2026-01-19T14:30:19Z

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Project	Deployment	Review	Updated (UTC)
spec	Ready	Preview, Comment	Jan 19, 2026 3:21pm

- Add custom middleware for automatic language detection - Map Chinese language codes (zh, zh-CN, zh-TW, zh-HK) to 'cn' - Redirect non-default language users to localized paths (/cn/) - Keep default language (en) users on clean URLs (/) - Store language preference in cookies for consistency - Add negotiator and type definitions as dependencies Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

- Remove unused @formatjs/intl-localematcher dependency - Extract SUPPORTED_LANGUAGES constant to reduce type assertion duplication - Use Object.fromEntries for more concise header conversion - Improve code readability and efficiency Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

- Add setLocaleCookie helper function with consistent cookie options - Set sameSite=lax and path=/ for security and consistency - Update comment for SUPPORTED_LANGUAGES constant - Ensure all cookie operations use the same configuration Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

- Handle root path (/) specially to avoid double slashes - Use precise regex for locale prefix removal - Ensure clean URLs: /cn instead of /cn/ - Improve path normalization logic Co-authored-by: huangyiirene <7665279+huangyiirene@users.noreply.github.com>

Copilot

Pull request overview

This PR implements browser language detection and automatic redirection for the homepage, replacing the default fumadocs i18n middleware with a custom implementation that maps Chinese language codes to /cn while keeping English users on / through internal rewrites.

Changes:

Custom middleware with Accept-Language header parsing using the negotiator library
Cookie-based language preference persistence with FD_LOCALE cookie
Locale-specific redirection logic: Chinese variants (zh, zh-CN, zh-TW, zh-HK) redirect to /cn, English stays on / with internal rewrite to /en

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 10 comments.

File	Description
apps/docs/middleware.ts	Replaced fumadocs default middleware with custom implementation for language detection, normalization, and routing
apps/docs/package.json	Added `negotiator` and `@types/negotiator` dependencies for Accept-Language parsing
pnpm-lock.yaml	Updated lockfile with new negotiator package and its type definitions

Files not reviewed (1)

pnpm-lock.yaml: Language not supported

Copilot · 2026-01-20T03:06:51Z

apps/docs/middleware.ts

+function getPreferredLanguage(request: NextRequest): string {
+  // Check cookie first
+  const cookieLocale = request.cookies.get(LOCALE_COOKIE)?.value;
+  if (cookieLocale && SUPPORTED_LANGUAGES.includes(cookieLocale)) {
+    return cookieLocale;
+  }
+
+  // Then check Accept-Language header
+  const negotiatorHeaders = Object.fromEntries(request.headers.entries());
+  const negotiator = new Negotiator({ headers: negotiatorHeaders });


The middleware creates a new Negotiator instance on every request even when a cookie is already set and valid. Consider skipping the Negotiator initialization if the cookie check at lines 56-59 returns early, by restructuring the code to only create the Negotiator instance after the cookie check fails.

Copilot · 2026-01-20T03:06:51Z

apps/docs/middleware.ts

+
+  if (pathnameHasLocale) {
+    // Extract the locale from the pathname
+    const locale = pathname.split('/')[1];


The middleware doesn't handle the case where pathname.split('/')[1] could be an empty string. If a pathname like //something is provided, locale would be an empty string, which could cause unexpected behavior. Consider adding validation to ensure the extracted locale is a non-empty string before using it.

Suggested change

const locale = pathname.split('/')[1];

const locale = pathname.split('/')[1] || '';

// If the extracted locale segment is empty or invalid, skip locale-specific handling

if (!locale) {

return NextResponse.next();

}

Copilot · 2026-01-20T03:06:51Z

apps/docs/middleware.ts

 * - Detects the user's preferred language from browser settings or cookies
 * - Redirects users to the appropriate localized version
+ * - For default language (en): keeps URL as "/" (with internal rewrite)
+ * - For other languages (cn): redirects to "/cn/"


The comment says "redirects to '/cn/'" (with trailing slash) but the actual implementation redirects to '/cn' (without trailing slash). The documentation should be corrected to accurately reflect the implementation.

Suggested change

* - For other languages (cn): redirects to "/cn/"

* - For other languages (cn): redirects to "/cn"

Copilot · 2026-01-20T03:06:51Z

apps/docs/middleware.ts

+function setLocaleCookie(response: NextResponse, locale: string): void {
+  response.cookies.set(LOCALE_COOKIE, locale, {
+    sameSite: 'lax',
+    path: '/',


The cookie is being set without an expiration time. This means it will be a session cookie that gets deleted when the browser closes. For a language preference, it would be better to set an explicit expiration (e.g., 1 year) so the preference persists across browser sessions.

Suggested change

path: '/',

path: '/',

// Persist language preference across browser sessions (1 year)

maxAge: 60 * 60 * 24 * 365,

Copilot · 2026-01-20T03:06:52Z

apps/docs/middleware.ts

+      return response;
+    }
+
+    return NextResponse.next();


When the pathname has a locale and it's not the default locale, the cookie is not being set. This means if a user manually navigates to a non-default locale URL (e.g., /cn), their preference won't be stored in the cookie. Consider adding a response with the cookie set in the else branch at line 111.

Suggested change

return NextResponse.next();

const response = NextResponse.next();

setLocaleCookie(response, locale);

return response;

Copilot · 2026-01-20T03:06:52Z

apps/docs/middleware.ts

+      // Remove locale prefix more precisely to avoid issues with partial matches
+      url.pathname = pathname.replace(new RegExp(`^/${i18n.defaultLanguage}(/|$)`), '$1') || '/';


The regular expression ^/${i18n.defaultLanguage}(/|$) could be vulnerable to ReDoS (Regular Expression Denial of Service) if i18n.defaultLanguage contains special regex characters. While the current value 'en' is safe, it would be safer to escape the language code using a helper function or use a simpler string-based approach. Consider using pathname.slice(i18n.defaultLanguage.length + 1) or escaping the language code.

Suggested change

// Remove locale prefix more precisely to avoid issues with partial matches

url.pathname = pathname.replace(new RegExp(`^/${i18n.defaultLanguage}(/|$)`), '$1') || '/';

// Remove default locale prefix using string operations to avoid regex issues

const defaultPrefix = `/${i18n.defaultLanguage}`;

if (pathname === defaultPrefix) {

url.pathname = '/';

} else if (pathname.startsWith(`${defaultPrefix}/`)) {

url.pathname = pathname.slice(defaultPrefix.length) || '/';

} else {

// Fallback: if for some reason the pathname doesn't match the expected pattern, keep it as is

url.pathname = pathname || '/';

}

Copilot · 2026-01-20T03:06:52Z

apps/docs/middleware.ts

+    const url = new URL(request.url);
+    // Handle root path specially to avoid double slashes
+    url.pathname = pathname === '/' ? `/${i18n.defaultLanguage}` : `/${i18n.defaultLanguage}${pathname}`;
+    return NextResponse.rewrite(url);


The cookie is not being set when the user's preferred language matches the default language. This means if an English-speaking user visits the site, their preference won't be stored, and the language detection will run on every subsequent request instead of using the cached cookie value. Consider setting the cookie even for the default language to improve performance on subsequent requests.

Suggested change

return NextResponse.rewrite(url);

const response = NextResponse.rewrite(url);

setLocaleCookie(response, preferredLanguage);

return response;

Copilot · 2026-01-20T03:06:52Z

apps/docs/package.json

    "@types/react": "^19.2.8",
    "@types/react-dom": "^19.2.3",
    "autoprefixer": "^10.4.23",
+    "negotiator": "^1.0.0",


The negotiator package is listed as a devDependency but it's imported and used in the middleware which runs at runtime. This package should be moved to the dependencies section instead of devDependencies to ensure it's available in production builds.

Copilot · 2026-01-20T03:06:53Z

apps/docs/middleware.ts

+  const negotiatorHeaders = Object.fromEntries(request.headers.entries());
+  const negotiator = new Negotiator({ headers: negotiatorHeaders });


Converting headers to a plain object using Object.fromEntries(request.headers.entries()) could potentially cause issues if there are duplicate header names (though unlikely with Accept-Language). Additionally, this creates a new object on every call. Consider passing the headers directly if the Negotiator API supports it, or at least document why this conversion is necessary.

Suggested change

const negotiatorHeaders = Object.fromEntries(request.headers.entries());

const negotiator = new Negotiator({ headers: negotiatorHeaders });

const acceptLanguage = request.headers.get('accept-language');

if (!acceptLanguage) {

return i18n.defaultLanguage;

}

const negotiator = new Negotiator({

headers: { 'accept-language': acceptLanguage },

});

Copilot · 2026-01-20T03:06:53Z

apps/docs/middleware.ts

+function setLocaleCookie(response: NextResponse, locale: string): void {
+  response.cookies.set(LOCALE_COOKIE, locale, {
+    sameSite: 'lax',
+    path: '/',


The cookie should also set the secure flag in production environments to ensure it's only transmitted over HTTPS. Consider adding secure: process.env.NODE_ENV === 'production' to the cookie options.

Suggested change

path: '/',

path: '/',

secure: process.env.NODE_ENV === 'production',

Initial plan

c74ab5a

Copilot AI assigned Copilot and huangyiirene Jan 19, 2026

vercel bot deployed to Preview January 19, 2026 14:30 View deployment

Copilot started work on behalf of huangyiirene January 19, 2026 14:30 View session

vercel bot deployed to Preview January 19, 2026 15:02 View deployment

vercel bot deployed to Preview January 19, 2026 15:07 View deployment

vercel bot deployed to Preview January 19, 2026 15:14 View deployment

vercel bot deployed to Preview January 19, 2026 15:21 View deployment

Copilot AI changed the title ~~[WIP] Add automatic language redirection for homepage~~ feat: implement browser language detection and auto-redirect for homepage Jan 19, 2026

Copilot AI requested a review from huangyiirene January 19, 2026 15:23

Copilot finished work on behalf of huangyiirene January 19, 2026 15:23

github-actions bot added documentation Improvements or additions to documentation dependencies Pull requests that update a dependency file size/m labels Jan 20, 2026

hotlong marked this pull request as ready for review January 20, 2026 03:02

Copilot AI review requested due to automatic review settings January 20, 2026 03:02

hotlong merged commit 2298e72 into main Jan 20, 2026
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feat: implement browser language detection and auto-redirect for homepage#30

feat: implement browser language detection and auto-redirect for homepage#30
hotlong merged 5 commits intomainfrom
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-    const locale = pathname.split('/')[1];
+    const locale = pathname.split('/')[1] || '';
+    // If the extracted locale segment is empty or invalid, skip locale-specific handling
+    if (!locale) {
+      return NextResponse.next();
+    }

	* - For other languages (cn): redirects to "/cn/"
	* - For other languages (cn): redirects to "/cn"

		// Remove locale prefix more precisely to avoid issues with partial matches
		url.pathname = pathname.replace(new RegExp(`^/${i18n.defaultLanguage}(/\|$)`), '$1') \|\| '/';

-      // Remove locale prefix more precisely to avoid issues with partial matches
-      url.pathname = pathname.replace(new RegExp(`^/${i18n.defaultLanguage}(/|$)`), '$1') || '/';
+      // Remove default locale prefix using string operations to avoid regex issues
+      const defaultPrefix = `/${i18n.defaultLanguage}`;
+      if (pathname === defaultPrefix) {
+        url.pathname = '/';
+      } else if (pathname.startsWith(`${defaultPrefix}/`)) {
+        url.pathname = pathname.slice(defaultPrefix.length) || '/';
+      } else {
+        // Fallback: if for some reason the pathname doesn't match the expected pattern, keep it as is
+        url.pathname = pathname || '/';
+      }

		const negotiatorHeaders = Object.fromEntries(request.headers.entries());
		const negotiator = new Negotiator({ headers: negotiatorHeaders });

-  const negotiatorHeaders = Object.fromEntries(request.headers.entries());
-  const negotiator = new Negotiator({ headers: negotiatorHeaders });
+  const acceptLanguage = request.headers.get('accept-language');
+  if (!acceptLanguage) {
+    return i18n.defaultLanguage;
+  }
+  const negotiator = new Negotiator({
+    headers: { 'accept-language': acceptLanguage },
+  });

	path: '/',
	path: '/',
	secure: process.env.NODE_ENV === 'production',

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