I'm french Canadian and I'm afraid I've never heard of an equivalent to this board in french...
I just googled it with every french term that I can imagine, haven't found anything... there are a few photo forums, but nothing pentax oriented.
There is this site, but it's just a website, not a forum:
Le site des amateurs de Pentax
If one cannot be found, may I suggest starting a french forum here? Many boards out there have a "foreign language" section with single Spanish, French, Italian... forums. I'm not sure there would be enough demand for that but it's a suggestion.
Pat