another step

client/middleware.ts

@@ -2,7 +2,7 @@ import createMiddleware from 'next-intl/middleware';
 import { type NextRequest, NextResponse } from 'next/server';
 import { routing } from './src/i18n/routing';
 import { COOKIE_NAMES } from './src/lib/cookies';
-import { PUBLIC_PATHS, ROUTES } from './src/constants';
+import { HEADER_NAMES, PUBLIC_PATHS, ROUTES } from './src/constants';
 
 const intlMiddleware = createMiddleware(routing);
 
@@ -39,7 +39,22 @@ export default function middleware(request: NextRequest) {
     }
   }
 
-  return i18nResponse;
+  // Detect locale from the normalized URL (next-intl always puts it at position 1)
+  const locale = routing.locales.find(
+    (l) => pathname === `/${l}` || pathname.startsWith(`/${l}/`),
+  ) ?? routing.defaultLocale;
+
+  const requestHeaders = new Headers(request.headers);
+  requestHeaders.set(HEADER_NAMES.LOCALE, locale);
+
+  const response = NextResponse.next({ request: { headers: requestHeaders } });
+
+  // Preserve response headers set by next-intl (e.g. Link: alternate hreflang)
+  i18nResponse.headers.forEach((value, key) => {
+    response.headers.set(key, value);
+  });
+
+  return response;
 }
 
 export const config = {