is there a French version of Urban Dictionary that you know of?
Sadly no… I’ve never found anything even close to what Urban Dictionary is.
I tried to work on a “French urban dictionary” tumblr, but it turned out to be a complete ordeal. I should have created a very specific theme to support that kind of huge content. I should have translated everything, because one of the bad points of Urban Dictionary is that the definitions themselves are slang and require a certain knowledge of the language. If I wanted to create a French Urban Dictionary, it would require translations and contexts, both in French and English. You can assume the workload, so I gave up and did the slang tag instead.
(However, if someone French wants to help, we could try to do it again…)