So, based on what we know so far… (thanks to Vehek from romhacking.net)
Font is stored in GB format (2bpp); roman characters + japanese kana begin at 0x00122480
And then comes kanji (in-game dialog is in Kanji, kana is only used for some texts)
Vehek says the text doesn’t seem to be stored as simple indexes (perhaps due to the the fact that characters are composed of 4 sprites? or that there are so many kanji, or both). Nonetheless, I think knowing the order the font is on will help figure out where sprites are loaded in memory.
My (first) plan is to eventually replace kanji tiles with 2 roman letter combinations, that may make things easier IF we manage to build equivalence table(s) in some way.
Thoughts? corrections? comment!