Do you know Japanese or are you otherwise slightly versed in programming?
Translating a whole game is usually a project of several months and is a bit outside the scope of a forum post. There is some documentation
http://gbatemp.net/threads/gbatemp-rom-hacking-documentation-project-rewritten-for-2012.73394/ and you might also like
http://www.romhacking.net/start/
I took at look at the original and the cross of venus special (apparently we can see "enhanced remakes" of a game released on the same console now). The special seems to have a whole bunch of ahx and adx files, these are a type of audio format but a known one.
What is not those is the usual DS binary stuff (only one overlay though for special and none for the original), mods (usually a type of video), a few called font (which appeared to have some basic fonts in) one .epb and the rest were .pack.
The sensible money has .pack as being an archive format and grabbing a bunch of them would have that appear to indicate the same thing. Most seemed to have a script file at the start, sometimes possibly as the only file, and then a bunch of file names. The data showed all the telltale signs of LZ compression but nothing I recognised.
Anyway it seems to be name, a section 0F hex long containing various things and then another name.
Anyway at first glance this does not look like an especially easy game to translate. Maybe if you have something to handle the pack files but other than that not so much.