fix: restore locale redirection using Next.js middleware

middleware.ts

@@ -0,0 +1,76 @@
+import { match as matchLocale } from "@formatjs/intl-localematcher"
+import Negotiator from "negotiator"
+import type { NextRequest } from "next/server"
+import { NextResponse } from "next/server"
+import { i18n } from "./lib/i18n/config"
+
+function getLocale(request: NextRequest): string {
+    // Check for saved locale in cookie first
+    const cookieLocale = request.cookies.get("NEXT_LOCALE")?.value
+    if (cookieLocale && i18n.locales.includes(cookieLocale as any)) {
+        return cookieLocale
+    }
+
+    // Negotiator expects plain object so we need to transform headers
+    const negotiatorHeaders: Record<string, string> = {}
+    request.headers.forEach((value, key) => {
+        negotiatorHeaders[key] = value
+    })
+
+    // @ts-expect-error locales are readonly
+    const locales: string[] = i18n.locales
+
+    // Use negotiator and intl-localematcher to get best locale
+    const languages = new Negotiator({ headers: negotiatorHeaders }).languages(
+        locales,
+    )
+
+    const locale = matchLocale(languages, locales, i18n.defaultLocale)
+    return locale
+}
+
+export function middleware(request: NextRequest) {
+    const pathname = request.nextUrl.pathname
+
+    // Skip API routes, static files, and Next.js internals
+    if (
+        pathname.startsWith("/api/") ||
+        pathname.startsWith("/_next/") ||
+        pathname.includes("/favicon") ||
+        /\.(.*)$/.test(pathname)
+    ) {
+        return
+    }
+
+    // Check if there is any supported locale in the pathname
+    const pathnameIsMissingLocale = i18n.locales.every(
+        (locale) =>
+            !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`,
+    )
+
+    // Redirect if there is no locale
+    if (pathnameIsMissingLocale) {
+        const locale = getLocale(request)
+
+        // Redirect to localized path
+        const response = NextResponse.redirect(
+            new URL(
+                `/${locale}${pathname.startsWith("/") ? "" : "/"}${pathname}`,
+                request.url,
+            ),
+        )
+
+        // Set locale cookie for future visits
+        response.cookies.set("NEXT_LOCALE", locale, {
+            maxAge: 60 * 60 * 24 * 365, // 1 year
+            path: "/",
+        })
+
+        return response
+    }
+}
+
+export const config = {
+    // Matcher ignoring `/_next/` and `/api/`
+    matcher: ["/((?!api|_next/static|_next/image|favicon.ico).*)"],
+}