Don't know if you already know about this but when installing a new translation och minibb you have to replace the file email_user_register_eng with for example email_user_register_swe if your forum is in Swedsish. You must also replace similar files.
- of course you should, that way multilingual board can be be also installed... it's not a bug.
Another problem I noticed now is that when I do a mistake like typing wrong password or forget giving a title to a topic the box "post new topic" becomes unclickable. Maybe temporary or something in firefox I don't know.
- be sure you have the latest release installed. It must contain bb_func_posthold.php file amongst other core scripts.