i googled too and apparently the game works on my firmware
if redubbing is not possible that sucks and there is nothing that can be done
but if anyone wants to work on redubbing and can somehow make this possible i can possibly help by finding the correct audio files
You can try this. Try to google or search how to get the at3+ files of the game, some of them should be the voices. Then extract the english voices from the DVD (there are millons of programs to do that), they would probably be in mp3 or wav and then you'll have to convert them to AT3 and somehow pack everything again. Try that with just a few boxes of text to see if it works (you know japanese, right? because that's the only way you can do all this xD). That's all I can tell you; I don't know how to
specificly extract anything or any specific software for all this (except the part of getting the voices from the DVD, which you probably already know). ....
I don't know, however if one at3+ file of the game equals one box of spoken dialogue or not; because if it doesn't then that would be a trouble. Also, I don't know if the PSP has some kind of register of their files, like, for example let's say that you modify (or replace) an audio file; maybe the PSP or the game has something (like a register) that checks the weight of the file (and maybe the new file isn't the same weight) and won't reproduce it unless it's 100% identical.
I already imagine someone from this forum who is a master at translating stuff reading this and thinking "WTF IS THIS GUY SAYING, THIS IS NONSENSE IT'LL NEVER WORK" xD, but hey, I'm just a noob throwing random ideas
Update: found this great tutorial:
http://forums.qj.net/guides-psp-mods-media/41612-how-make-at3-files.html . It would be useful if what I said above works