title: Symfony 3 get all avaliable locales
body: <p>Have some trouble getting all available locales in Symfony 3. 
  The idea is to create a custom language switcher.</p>
  
  <p>I have</p>
  
  <pre><code>parameters:
  locale: en
  app.locales: en|fr|ru
  </code></pre>
  
  <p>I can get requested locale or user stored in session locale.
  But how can i get all parameters.app.locales in Service of Controller on finally in Twig? So that i can have ar array like en|fr|ru and so on.</p>
  
  <p>Thanks.</p>