tampering between jp/us version of a game, possible at all?

hi everyone i'm new here, with a problem at hand.

the game in question is Luminous Arc, #846 for the JP version and #1329 for the US version.

obvious difference is the jp version is in japanese and us version in english.

what i'm trying to do is, somehow combine the 2 together, and get one with the japanese audio (basically dialogues) and the us text (subtitles, if you will).

i have tried finding the dialogue texts from the US version (with a hex editor, in the .nds file) and replacing the same section of the .nds file of the japanese version. there was some variation in length, but i'm sure nothing else got replaced.

afterwards, i trimmed the file to exactly the same size as the original game file's size. when i run it, R4 shows that it's loading, but after that i just get a blank screen.

so now i'm wondering if there's anything i've done wrong/could do/etc, or whether this is even possible at all.

thanks in advanced!
-meh

ps. i have the offsets for the (i'm guessing) dialogues chunk of the .nds file if necessary.