I'd be on it right now were it not for real life getting in the way...
You've done most of the work by the looks of it, with ROM locations and what have you. I'll try to have a look in a few hours.
EDIT: Okay, I see a big problem immediately: screen space. In the detailed conversations, there's no nice big text window to fit a big translation in, just one tiny line along the bottom, 28 characters across. You can run onto the next line if you want, but it's probably in the CRT danger zone which I'd rather keep out of. The menus only use three characters of course, but that's less of a problem (still not good though). The little chats out in the open aren't so bad since the window can be expanded (with some effort).
With the lack of screen space, ROM space is less of an issue: there is lots of empty space in there, but it'd be hard to use given the bank swapping required. A DTE routine would probably be more than satisfactory here, since there can't be much English text anyway, and the original text is uncompressed. The pointers are simple, but the mapper uses 8KB ROM banks, so you're limited to whatever bit of the ROM has been loaded in at that point.
All in all, putting text into the game is easy. Putting your GOOD text in, however... quite a challenge.