Use language setting of users when logging in.

config/routes.yaml

@@ -1,3 +1,10 @@
 #index:
 #    path: /
 #    controller: App\Controller\DefaultController::index
+
+# Redirect every url without an locale to the locale of the user/the global base locale
+redirector:
+    path: /{url}
+    requirements:
+        url: ".*"
+    controller: App\Controller\RedirectController:addLocalePart