title: Translate error message of login form
body: <p>I use FOSUserBundle login form and i would like translate errors messages. These messages are launched here: <strong>vendor/symfony/src/Symfony/Component/Security/Core/Authentication/Provider/DaoAuthenticationProvider.php</strong></p>
  
  <pre><code>protected function checkAuthentication(UserInterface $user, UsernamePasswordToken $token)
      {
          $currentUser = $token-&gt;getUser();
          if ($currentUser instanceof UserInterface) {
              if ($currentUser-&gt;getPassword() !== $user-&gt;getPassword()) {
                  throw new BadCredentialsException('The credentials were changed from another session.');
              }
          } else {
              if (!$presentedPassword = $token-&gt;getCredentials()) {
                  throw new BadCredentialsException('The presented password cannot be empty.');
              }
  
              if (!$this-&gt;encoderFactory-&gt;getEncoder($user)-&gt;isPasswordValid($user-&gt;getPassword(), $presentedPassword, $user-&gt;getSalt())) {
                  throw new BadCredentialsException('The presented password is invalid.');
              }
          }
      }
  </code></pre>
  
  <p>I've write <strong>app/Resources/translations/validators.fr.yml</strong></p>
  
  <pre><code>"The presented password cannot be empty.":      "Veuillez saisir un mot de passe."
  </code></pre>
  
  <p>I've write <strong>app/Resources/translations/messages.fr.yml</strong></p>
  
  <pre><code>"The presented password cannot be empty.":      "Veuillez saisir un mot de passe."
  </code></pre>
  
  <p>But it doesn't work.
  Other translation are working (=>fr), but i've problem with these messages.</p>
  
  <p>Special procedure for these messages ?</p>