code: private function addFrontendRoute(RouteCollection $routes, array $defaults): void
      {
          $route = new Route('/{alias}'.$this->urlSuffix, $defaults, ['alias' => '.+']);
  
          $this->addLocaleToRoute($route);
  
          $routes->add('contao_frontend', $route);
      }
docs: Adds the frontend route, which is language-aware.