Nerdiness, even in the U.S., has nothing to do with intelligence and everything to do with behavior. "Smart kids" are despised not because they're smart, but because of manifold other traits like bad hygiene, looking down on others, sucking up to teachers, etc.
Part of learning big words, is learning when to use them. Kids who use big words in school aren't despised for the big words, but for using them inappropriately.
You should embrace your hobbies completely and be passionate about them. This is a BIG TURN ON to girls, regardless of the hobby. The key is to do it in a non-weird way. There WILL be certain conversations that come up. Don't avoid them- learn to predict them and roll with them.
I'm a mathematician, and mathematics is even "worse" than Japanese as far as telling people what you're interested in. I used to avoid bringing it up, and change the subject when it was brought up. I was very apologetic about it. This was a major turn-off: girls could tell that I was ashamed of my own passions. It's incongruous. Now, when the subject comes up, I say something like.. "Ever see Good Will Hunting? That movie's based on me

" If telling people about Japanese leads them to talk about Japanese girls, EMBRACE IT! Say something like.. "hell yeah man Japanese chicks are the hottest babes on earth. The other day I met this jgirl at the supermarket and I started talking to her in japanese and she was alllll over me" Talking about hot girls will win you lots of social points among guys, and girls will be impressed that you can be passionate about something so stigmatized.
I find I have EXTREMELY good results in night clubs (phone numbers, makeouts, etc) when I start talking about languages in general. Like I'll start talking to a girl saying things like "One of these days I wanna learn every language on earth" etc. etc. Coming from a well-dressed, fit guy, this totally blows the girls minds because hey, you're not a meathead like everyone else in the club. It's $$$MONEY$$$.
If you're suffering socially due to "nerdiness", I *guarantee* you it's not because of the specific things you're nerdy about (japanese, star wars, math, or anything). It's hard and you won't like me telling it to you, but nerds suffer because they're socially inept, they dress bad and they smell bad and they're out of shape. The good news though is these things can be fixed.
I'm going off on a tangent. Back to the subject at hand.. the point is, don't hide your passions, embrace them and use them as your greatest asset.
Edited: 2008-06-04, 6:05 pm