If I may make a small request: I would appreciate it if, when a question or answer is posted in a language other than English, someone with the requisite multilingual ability could add a translation in English to the content of the post, because:
I believe there are people here who are not professional mathematicians and do not know (for example) French, but would be very interested in the content of the question or answer posted if only they could read it.
If a similar or related question gets posted in English, it would not help to direct the asker to a previous question that he or she cannot even read. In particular, closing as exact duplicate would be unfortunate.
Certainly one can always resort to Google Translate, but a translation by machine is not necessarily accurate, and is often taxing to read.
(Right now, someone has helpfully provided a translation of the question into English in the comments, but it would be nice if it were added to the question itself, as comments do not show up in search.)