Well, the amount of 3DS themes in Japan is like three-four times of what we got in North America, and a lot of them are Japan-centered obviously.
Though, I'm remembering all the good times when New Leaf was only available in Japan and South Korea, and it was especially funnier when I had a very limited knowledge of the language at that time and we were considered as some kind of god.
I also got some more interesting 3DS Japanese-exclusive games, such as E.X. Troopers and Puyo Puyo Tetris. I'm pretty sure these are fun titles that don't demand too much of language knowledge in order to enjoy them. Though, reading them is nevertheless a fun thing to do.