Support localized messages in validation messages

[LaChope]

We must use internationalization as it is already set up (localized labels), but not implemented.

Well, you get here a localized label of the question, but you do not translate the message here. I believe that to do it effectively and systematically, you would need to do template i18n strings ...
I believe this is quite hard to implement and we can live without it for a while in AVA, thus maybe it makes sense to create ticket out of it.

Originally posted by @blcham in #207 (comment)