fix: localize 404 and ensure header when no lang

middleware.ts

@@ -1,6 +1,6 @@
 import { NextMiddleware, NextResponse } from "next/server"
 
-import { findLang } from "./constants/languages"
+import { findLang, Lang } from "./constants/languages"
 import * as authRequired from "./middlewares/authRequired"
 import * as cmsContent from "./middlewares/cmsContent"
 import * as currentWebLogin from "./middlewares/currentWebLogin"
@@ -16,8 +16,10 @@ export const middleware: NextMiddleware = async (request, event) => {
     // Without it we shortcircuit early.
     // We use middleware-error route because notFound() requires a root layout
     // which we do not want. We can move to that once all Current stuff is gone.
+
+    // Default to English if no lang is found.
     return NextResponse.rewrite(
-      new URL(`/${lang}/middleware-error/404`, request.nextUrl),
+      new URL(`/${Lang.en}/middleware-error/404`, request.nextUrl),
       {
         status: 404,
         statusText: "Not found",