Connect American Nintendo 3ds with German?

My girlfriend and I were about to play Mario Kart 7 together, but she has an American Nintendo 3ds and I have a German one. We found each other locally via the friend list, but it does not work to connect us locally at mario kart. What can that be?

It may be because there's a regional lock - i.e. H. The German consoles can only recognize the PAL version of a game - whereas the American consoles / games are sold as NTSC versions.

From the Nintendo 3DS upwards, the games / handhelds have a region lock (also the 2DS)

That means you can't play American or Japanese games on a European device.