The customer requested to improve or add missing login exception translations.

For example, the customer indicated the exception:
https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Publish/Core/MVC/Symfony/Security/Authentication/RepositoryAuthenticationProvider.php#L42
which is not translated on the frontend.

Moreover, the customer suggested changing the way of translating exception messages. Right now translations are done in templates and eZ Platform uses message strings instead of keys. As mentioned by the customer it is not recommended way to do translations according to the Symfony documentation (http://symfony.com/doc/2.8/best_practices/i18n.html):

Always use keys for translations instead of content strings.