It's very time consuming to do optical character recognition and manual correction.
The best thing, I guess, would be if people could contribute with each language's subs that they want to be included. Of course, those subs will be put on the BD as is, which means if they aren't corrected they'll be on the BD just as bad as they are.
If sending us subs, make sure they're in srt-format and synched to the NTSC GOUT. (It also works if they're synched to Harmy's despecialized editions)