Yes there is Wwoofing in Japan, I am a member but never tried it
.: WWOOF Japan :..
As french citizen you can also participate in the Working holiday scheme
MOFA: The Working Holiday Programmes in Japan ,
Japan Association for Working Holiday Makers wich allows you to stay and work in Japan for up to a year. I did a year and i can give you some more information if you want to. But be aware that most jobs don´t pay to good so wwoofing is maybe better.