This wont work.
The major problem is this; you will write the song, and then English lyrics over the top, which will be in time with the music. Then it will be translated into Japanese, and you will be hard put to make it fit with the song.
Also, the best way to learn Japanese is to hit the books.
And one more thing, you say you are going to live in Japan early 2009? You definitely need to learn the language yourself to do that.
I suggest you listen to Japanese bands, and take apart their songs. You will be able to see how Japanese songs are put together. Learn to read passages on the net in Japanese, and understand them. Then try writing songs.
I suggest that you visit Japan for maybe a couple of months in early 2009, to see how your Japanese is coming along and whether or not you can survive there. You need to know common phrases like 'where is the milk, I am sure I bought some earlier at the store' rather than song lyrics, such as 'My love is the only thing to me, la-dada' (or whatever)
Oh, and last point, welcome to JREF. Hope you make friends here.