I created an application which was not intended to have translations, but now I decided to add this feature. The problem is that all my routes look like this:
I think you need a custom loader extending the classic config loader (Symfony\Component\Config\Loader\Loader) and manipulate the pattern
http://symfony.com/doc/current/cookbook/routing/custom_route_loader.html
check the first example, i haven't tried it yet, but i'm quite sure it will fit your problem.