Huge love for the japanese culture. In France, the japanese culture became popular in the late 80's, and it became HUGE in the early 90's thanks to the TV show "Club Dorothée", a kid's show that was broadcasted on the principal french channel : TF1. Thanks to the Club Dorothée, french kids learned the existence of and started to love some huge japanese animes such as Dragon Ball, Dr Slump, City Hunter, Hokuto no Ken, Saint Seiya, etc... This show was the most popular kid's show in France, and it almost broadcasted only japanese animes (along with some disney stuff such as Duck Tales, but really, 80% were japanese animes and even some Super Sentai show, before even the Power Rangers !) Mangas started to be sold on France and it was a success.
Nintendo of course also had its part in this love for the japanese culture, the NES was a cultural phenomenon in France.
Then, in the late 90's, "Canal +" started to broadcast some more mature animes such as Neon Genesis Evangelion, Cobra, Cowboy Bebop and GTO.
France also started to discover Miyazaki's films.
The PS1 was a success, with FFVII and MGS having a huge impact on the french players. (Just like everywhere else on the world, tho)
France also started to discover a new kind of japanese cinema thanks to Takeshi Kitano : Sonatine, Hana Bi and Kikujiro (directed by Kitano) in the late 90s all met huge love from the french critics, and Battle Royale started to become a cult classic thanks to the performance of Takeshi Kitano in the early 2000s.
Then, the Big 3 happened : Naruto, Bleach and One Piece all started around the same time, and they were all huge success in France. At this point there was no turning back, no matter their age, all french would casually consume japanese culture.
(The japanese food is also really popular but I think it's the case pretty much everywhere in the world lol, or at least in Europe.)
I think all of this explains how, by the early 2000s, France became one of the most japanese culture's consumer of the world, and why Nintendo has always been really popular here, even during the N64, Gamecube and Wii U era.
