feat(i18n): enhance localization support with new languages(zh-tw/ja)

middleware.ts

@@ -1,6 +1,6 @@
 import { auth } from "@/lib/auth"
 import { NextResponse } from "next/server"
-import { i18n } from "@/i18n/config"
+import { i18n, type Locale } from "@/i18n/config"
 import { PERMISSIONS } from "@/lib/permissions"
 import { checkPermission } from "@/lib/auth"
 import { Permission } from "@/lib/permissions"
@@ -63,7 +63,9 @@ export async function middleware(request: Request) {
   const hasLocalePrefix = i18n.locales.includes(maybeLocale as any)
   if (!hasLocalePrefix) {
     const cookieLocale = request.headers.get('Cookie')?.match(/NEXT_LOCALE=([^;]+)/)?.[1]
-    const targetLocale = (cookieLocale && i18n.locales.includes(cookieLocale as any)) ? cookieLocale : i18n.defaultLocale
+    const acceptLanguage = request.headers.get('Accept-Language')
+    const preferredLocale = resolvePreferredLocale(cookieLocale, acceptLanguage)
+    const targetLocale = preferredLocale ?? i18n.defaultLocale
     const redirectURL = new URL(`/${targetLocale}${pathname}${url.search}`, request.url)
     return NextResponse.redirect(redirectURL)
   }
@@ -71,6 +73,61 @@ export async function middleware(request: Request) {
   return NextResponse.next()
 }
 
+function resolvePreferredLocale(cookieLocale: string | undefined, acceptLanguageHeader: string | null): Locale | null {
+  if (cookieLocale && i18n.locales.includes(cookieLocale as Locale)) {
+    return cookieLocale as Locale
+  }
+
+  if (!acceptLanguageHeader) return null
+
+  const candidates = parseAcceptLanguage(acceptLanguageHeader)
+  for (const lang of candidates) {
+    const match = matchLocale(lang)
+    if (match) {
+      return match
+    }
+  }
+
+  return null
+}
+
+function parseAcceptLanguage(header: string): string[] {
+  return header
+    .split(',')
+    .map((part) => {
+      const [lang, ...params] = part.trim().split(';')
+      const qualityParam = params.find((param) => param.trim().startsWith('q='))
+      const quality = qualityParam ? parseFloat(qualityParam.split('=')[1]) : 1
+      return { lang: lang.toLowerCase(), quality: isNaN(quality) ? 1 : quality }
+    })
+    .sort((a, b) => b.quality - a.quality)
+    .map((entry) => entry.lang)
+}
+
+function matchLocale(lang: string): Locale | null {
+  const exactMatch = i18n.locales.find((locale) => locale.toLowerCase() === lang)
+  if (exactMatch) return exactMatch
+
+  const base = lang.split('-')[0]
+
+  // Handle Chinese variants with explicit regions or scripts
+  if (base === 'zh') {
+    if (lang.includes('tw') || lang.includes('hk') || lang.includes('mo') || lang.includes('hant')) {
+      return 'zh-TW'
+    }
+    if (lang.includes('cn') || lang.includes('sg') || lang.includes('hans')) {
+      return 'zh-CN'
+    }
+    // default Chinese fallback
+    return 'zh-CN'
+  }
+
+  const baseMatch = i18n.locales.find((locale) => locale.toLowerCase().split('-')[0] === base)
+  if (baseMatch) return baseMatch
+
+  return null
+}
+
 export const config = {
   matcher: [
     '/((?!_next|.*\\..*).*)', // all pages excluding static assets
@@ -80,4 +137,4 @@ export const config = {
     '/api/config/:path*',
     '/api/api-keys/:path*',
   ]
-} 
+}