You never noticed that before?! I always thought it was cool because they actually said something for once.
Duke Serkol and I talked about this a long time ago, it's definately Japanese because the game is made in Japan and all the other voice-overs are in Japanese. If you can record the sound off your computer and slow it down, they don't all speak at the same time, so five people shouting at the same time also kind of makes it unclear for those of us who don't speak Japanese.
In summation, I have no idea.