Symfony3 can't create translated routes with router in service

I'm trying to build a language switcher into my main navigation, which is created by the KNPMenuBundle. Translations are done with the JMSTranslationBundle. Both work fine.

I want to create a language switcher with my menu builder, but the generation of the correct routes gives me some headaches.

This is my service:

class MenuService
{
    private $factory;
    private $translator;
    private $router;

    public function __construct(FactoryInterface $factory, Translator $translator, Router $router)
    {
        $this->factory = $factory;
        $this->translator = $translator;
        $this->router = $router;
    }

    public function createMainMenu(RequestStack $requestStack, array $languages)
    {
        // Language Switcher - $languages === ['en', 'de']
        $request = $requestStack->getCurrentRequest();
        $routeName = $request->get('_route');

        $menu->addChild('menu.language', array(
            'uri' => '#',
            'label' => '<i class=\'fa fa-flag-checkered\'></i> '.$this->translator->trans('menu.language.main'),
            'extras' => array('safe_label' => true)
        ))
            ->setAttribute('class', 'dropdown singleDrop')
            ->setChildrenAttribute('class', 'dropdown-menu dropdown-menu-left')
        ;

        foreach ($languages as $language)
        {
            $menu->getChild('menu.language')->addChild('menu.language.'.$language, array(
                'route' => $this->router->generate($routeName, array_merge($request->get('_route_params'), ['_locale' => $language]))
            ));
        }
    }

And this is my service definition

menu_builder:
    class: AppBundle\DependencyInjection\MenuService
    arguments: ['@knp_menu.factory', '@translator.default', '@jms_i18n_routing.router']

menu.main:
    class: Knp\Menu\MenuItem
    factory: ['@menu_builder', createMainMenu]
    arguments: ['@request_stack', '%locales%']
    scope: request
    tags:
      - { name: knp_menu.menu, alias: main }

If I inject the Router provided by the JMSTranslationBundle, I receive the following error:

An exception has been thrown during the rendering of a template ("Unable to generate a URL for the named route "/en/" as such route does not exist.").

If I'm using the default router of symfony I'm getting this error message:

An exception has been thrown during the rendering of a template ("Unable to generate a URL for the named route "homepage" as such route does not exist.").

When I debug the router on the console, this is the output:

  en__RG__homepage                                         ANY        ANY      ANY    /en/                                                 
  de__RG__homepage                                         ANY        ANY      ANY    /de/  

Which router must be used to get the routing to work?