Problems with mandatory fields and error messages.

Hello since I replaced the English language by the French language, the error messages no longer appear on my site, I use the meeting theme, to create an ad I put the obligatory pictures and it is that users can validate their ads (even if they have not put the photo) while the field and binding. I already tested, I put the first version of the website in English that you sold me, but when I replace at least one word in the admin error messages or compulsory field no longer work, this is not normal?
To the registration form is the same, the error messages are not displayed, users can create the same account if it leaves an empty field.
Thank you for your help please