The problem is, I'm not really skilled in hacking or programming, though I do know how to do easy things with guides. I've looked at the ROM using DSlazy, and the although both the Japanese and USA rom have both 64 MB, when opened with the program, the Japanese rom contains additional folder "voices" inside the sound folder, having about 27 MB. I've tried simply putting the voices folder inside the USA rom and repacking it, however it has no effect, and the rom is even by several MB smaller! So the new one has about 59 MB, however it still works.
I've also tried putting the "font" folder from J into USA rom, however after the intro the game freezes with black screens. If I knew where the translation is located, maybe it could be fairly easy to put the English text there, though since I'm not a romhacker, I can't say that for sure.
Would anyone mind having a look at the rom and say whether it's possible to either put the voices into the USA rom or the english text into the J apanese rom and how easy/difficult it would be?