There is a bundle for routing internationalization called BeSimpleI18nRoutingBundle but it is not available for symfony 4 right now.

Core symfony implementation

With core symfony you could use multiple routes for each controller, that would have a {_locale} parameter with default value, here the problem would be that two different URLs would be returning the same page.

e.g /test would be the same as /test/en

This might cause problems with SEO

here how the annotations would look like if you wish to implement this method

/**
 * @Route("/test/{_locale}", defaults={"_locale"="en"}, requirements={"_locale":"en"}, name="default_en")
 * @Route("/δοκιμή/{_locale}", defaults={"_locale"="el"}, requirements={"_locale":"el"}, name="default_el", options = {"utf8": true})
 * @Route("/tester/{_locale}", defaults={"_locale"="fr"}, requirements={"_locale":"fr"}, name="default_fr")
 */
public function test($_locale)
{
    return new Response("Your current locale is : $_locale");
}

Dynamic Route

Another option is to create a Routing Service that would apply your logic. Here is an example.

this would be the controller that handles all the paths

Controller

namespace App\Controller;

use Symfony\Component\Routing\Annotation\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;
use App\Service\Router;

class RouterController extends Controller {

    /**
    * @Route("/{path}", name="router", requirements={"path" = ".+"})
    */
    public function router($path,Request $request,Router $router) {

        $result=$router->handle($path);

        if($result){
            $result['args']['request']=$request;
            return $this->forward($result['class'], $result['args']);
        }


        throw $this->createNotFoundException('error page not found!');        
    }

}

This Controller Action depends on a service called Router so you will have to create a Router service that would return the an array (you can change it to return a custom object) with keys class and args that would be used to forward the request to a controller action.

Service

/src/Service/Router.php

Here you should implement a function called handle and you can apply any logic to it

here is a basic example

namespace App\Service;

class Router
{

    public function handle($path)
    {
        switch ($path) {
            case "test":
                return [
                    "class" => "App\Controller\TestController::index",
                    "args"  => [
                        "locale" => 'en'
                    ]
                ];
            case "tester":
                return [
                    "class" => "App\Controller\TestController::index",
                    "args"  => [
                        "locale" => 'fr'
                    ]
                ];
            default:
                return false;
        }
    }
}

The code above would forward the request to TestController::index function and will add as parameter to that function the locale variable and also it will include the Request object

You could store the routes in a yaml file or database or any other location you like. You can manipulate the $path variable to extract information about id, page etc.