If I'm not mistaken, the movie is entirely in Aramaic and Hebrew, with some Latin thrown in.
How many people do you know who speak Aramaic? Yeah, I thought so.
He did, however, show a translated version to some Christian groups (but won't let the ADL see it). It will have to be translated for mainstream audiences, but I imagine with its length (approximately 4 hours) and surrounding controversy, many theaters won't take it. Gibson knows it won't make a profit--it is his labor of love.
I'd actually like to see it. Not as a religious person, but someone who loves history and film.
You can see the trailer here:
The Passion entry on IMDB