@Silvere
 
I'm not seeing the same issues. Just downloaded the latest French language pack fr.phar from our website, installed it on the latest develop-next (which is basically v1.14.1 with latest bug fixes), set my Primary Language to French, cleared the cache and voila I can see everything in French.

Maybe you're missing the phar, mbstring, and/or intl extensions for PHP? Or maybe the browser cache is in the way and you need to clear it?
Cheers.