title: Translate the Flash Message
body: <p>I'm trying to translate the flash message I sent, if a form is succesful. 
  The normal request looks like this:</p>
  
  <pre><code>$request-&gt;getSession()-&gt;getFlashBag()-&gt;add(
              'notice',
              'Your E-Mail has been sent.'
          );
  </code></pre>
  
  <p>So I tried to translate the message with the following variable: </p>
  
  <pre><code>$request-&gt;getSession()-&gt;getFlashBag()-&gt;add(
              'notice',
              'contact.message.email_has_been_sent'
          );
  </code></pre>
  
  <p>After sending the form the message shows "contact.message.email_has_been_sent". So it didn't found the translation, but the variable is right. I tested it inside a template file. 
  Has anyone an idea, how I could fix this? I didn't found anything useful yet. </p>