How to get the _locale variable inside in a Symfony layout?

I'm working with Symfony 2 on a site which having 2 languages, and I want to change patterns of my routes depending on user locale language !

Example:

user_login_en:
    pattern:  /en/user/login.html
    defaults: { _controller: SfErrorsAppBundle:User:login, _locale: en }

user_login_fr:
    pattern:  /fr/utilisateur/connexion.html
    defaults: { _controller: SfErrorsAppBundle:User:login, _locale: fr}

Inside a template, this is not difficult, i just have to pass the $this->get('session')->getLocale() from the controller to the template...

To work, I have to call my routes:

$router->generate('user_login_'.$locale, array());

But inside my layouts, I have of course a menu, and sidebars, which have links... So I want to get the locale variable to use it ! So my question is simple: how to get this variable inside a "layout" template ? Otherwise, have you got any idea to change the pattern depending on the language ?

The reasons are that I want beautiful routes for all users, whether they're english or french... And also for a SEO reason !