
Extract the original Japanese.vpm or whatever language. Then play each wav file and write down what each one says. After doing so, try to use the American_English wav files by replacing the japanese ones.
Dunno if it will work with japanese, cause I'm not sure of the phrase structures... but, what about other languages?
If just replacing won't work, then you'll have to work with Voice Editor's langid changer... and phrase changer. I haven't looked into that, cause I don't need to... but if I were you (and I repeat, IF I had the time - cause it'll take time -), I'd start from there... and see what happens.
Good luck!
Cheers.