Maximilien, we prepare French po file and add it to our translation system now you can register on http://translate.userecho.com then we grant you needed rights and you can help us with French version, also we can make all translations with google translate API and you check it
We just launched our new collaborative translation portal for UserEcho
http://translate.userecho.com/
Find out more details in our blogpost
http://blog.userecho.com/topic/149204-we-are-launched-userecho-collaborative-translation-portal/
And feel free to participate!