title: Sonata Admin - default_locale overwritten by fallback
body: <p>I'm trying to set Sonata pages locale to different value than my main application.</p>
  
  <p>I have in my <code>config.yml</code>:</p>
  
  <pre><code>    parameters:
          locale: ru
      framework:
          translator: { fallbacks: ["%locale%"] }
      sonata_translation:
          locales: [en, de]
          default_locale: en
  </code></pre>
  
  <p>I expected to have main page in Russian and admin pages in English, but all pages are in Russian.</p>
  
  <p>How can I change default language of Sonata Admin pages?</p>