title: symfony2: pseudo locale (auto-)detection
body: <p>I have googling this for weeks now and i can't find a nice answer and uique way to do this.
  I have a symfony2 application that is using FOSUserBundle. The app is available in different languages.</p>
  
  <p>What i would like is to have an unique way to handle the locale detection. Since it has been moved from the session to the request i don't see a clear way to achieve that. </p>
  
  <p>step a) user is not logged, maybe 1st time we saw it. Take the locale from the request header Accept-Language:en-US,en;q=0.8,fr;q=0.6 (for instance). Serve the user a localized version of login page</p>
  
  <p>step b) user is now loggued in. of course we still serve him is prefered language based on the same header</p>
  
  <p>So far i have done this using ResponseListner but it seems it won't work for the 1st request  and have troubles with the FOSuser login page.</p>
  
  <p>Any help with samples would be very appreciated.</p>