[Routing] Document the effect of setting locale on a route with loc…

…ale prefixes

routing.rst

@@ -2416,6 +2416,54 @@ with a locale. This can be done by defining a different prefix for each locale
  ;
  };
 
+.. tip::
+
+ If the special :ref:`_locale <routing-locale-parameter>` routing parameter
+ is set on any of the imported routes, that route will only be available
+ with the prefix for that locale. This is useful when you want to import
+ a collection of routes which contains a route that should only exist
+ in one of the locales:
+
+ .. configuration-block::
+
+ .. code-block:: php-annotations
+
+ // src/Controller/CompanyController.php
+ namespace App\Controller;
+
+ use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+ use Symfony\Component\HttpFoundation\Response;
+ use Symfony\Component\Routing\Annotation\Route;
+
+ class CompanyController extends AbstractController
+ {
+ /**
+ * @Route("/about-us/en-only", locale="en", name="about_us")
+ */
+ public function about(): Response
+ {
+ // ...
+ }
+ }
+
+ .. code-block:: php-attributes
+
+ // src/Controller/CompanyController.php
+ namespace App\Controller;
+
+ use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+ use Symfony\Component\HttpFoundation\Response;
+ use Symfony\Component\Routing\Annotation\Route;
+
+ class CompanyController extends AbstractController
+ {
+ #[Route('/about-us/en-only', locale: 'en', name: 'about_us')]
+ public function about(): Response
+ {
+ // ...
+ }
+ }
+
 Another common requirement is to host the website on a different domain
 according to the locale. This can be done by defining a different host for each
 locale.