Symfony @Route注解i18n:是否有可能对未显式声明的语言进行后备？

use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Matcher\RequestMatcherInterface;
use Symfony\Component\Routing\RouterInterface;

class I18nFallbackRouteMatcher implements RequestMatcherInterface
{
    private $router;
    private $fallbackLocale;

    public function __construct(RouterInterface $router, string $fallbackLocale)
    {
        $this->router = $router;
        $this->fallbackLocale = $fallbackLocale;
    }

    public function match(Request $request): array
    {
        $match = $this->router->match($request);

        if ($match === null && $request->getLocale() !== $this->fallbackLocale) {
            $request->setLocale($this->fallbackLocale);
            $match = $this->router->match($request);
        }

        return $match;
    }
}

# config/routes.yaml
app:
    resource: ..
    type: annotation
    prefix: /{_locale}
    requirements:
        _locale: en|fr|de
    defaults:
        _locale: en

# config/services.yaml
services:
    app.i18n_fallback_route_matcher:
        class: App\I18nFallbackRouteMatcher
        arguments:
            $router: '@router'
            $fallbackLocale: 'en'

# config/packages/routing.yaml
framework:
    router:
        request_matcher: app.i18n_fallback_route_matcher