Maybe I was not accurate enough in my request ^^.
In fact, I'd like someone with a Japanese Gen4 game to use the Pokeshifter from this game to his or her Black or White game. As Pokeshifter requires 2 games from the same region, this is the only way:
I transfer my Pokes to someone's Japanese Plat, Diamond, HGSS etc... via Wifi, this person transfer them via Pokeshifter (local) to his Black/White, and then can trade them back to me via Wifi, on my White ^^. A bit complicated yes lol. But this is the only way I have for now.