Haie
Krita is delivered with English - US language for its interface. How to download French language?

I'm sorry, but that is not available at the moment. I haven't had time to do language packs for Windows.

Hi,
How can we help to translate in French ?
Which compiler must I use ?
Can it be compiled on Windows system ?

You can contact the french translation team here: http://i18n.kde.org/team-infos.php?teamcode=fr. You don't need to compile krita to help translating it, but some of the tools might be linux specific, I'm not sure about that.