Hi,
The issue of e-mail is solved, but not the question of language.
"You must translate core, theme and plugins." : on the screenshot, you can see the translation file of apparently the core, and on line 242 you can see "Publish your ad for free" translated into "publiez votre annonce gratuite" (so, it looks like the translation is done at least for that part) but it does not appear on the home page of my site where this and other things remain in English.
Thanks for help. This platform is important to our community.