I'd like to ask for recommandations of critique/workshop websites in French.
Would it be more on-topic here or on French SE?
Generally speaking, are questions about documentation, websites, books, etc. in other languages than English accepted ?
Questions and answers on Writers.SE are expected to be in English. However, the scope of those questions and answers is worldwide and multi-lingual; we are not limited to questions about work that will be written in English.
So if you are looking for French-language critique sites, feel free to ask here, in English. Be sure to specify the characteristics you're looking for so it doesn't become a broad, opinion-poll question. You probably have restrictions related to price, genre, publicity level (publishing your work unsecureed on the Internet isn't always good), community size, and probably other things, so try to describe in some detail what you're looking for.