core-bundle/src/Routing/FrontendLoader.php
private function addFrontendRoute(RouteCollection $routes, array $defaults): void
    {
        $route = new Route('/{alias}'.$this->urlSuffix, $defaults, ['alias' => '.+']);

        $this->addLocaleToRoute($route);

        $routes->add('contao_frontend', $route);
    }
private function addFrontendRoute(RouteCollection $routes, array $defaults): void
    {
        $route = new Route('/{alias}'.$this->urlSuffix, $defaults, ['alias' => '.+']);

        $this->addLocaleToRoute($route);

        $routes->add('contao_frontend', $route);
    }
Adds the frontend route, which is language-aware.