Board Thread:Love Live! School Idol Festival Lounge/@comment-29927505-20160909231220/@comment-11148831-20160910072639

Did you mean having both JP and EN on the same device? If yes, then it's possible to have both in one device.

Did you mean transferring your EN account to JP? If yes, then no, it's not possible to transfer your EN account to JP server.

For your last question, no, EN codes do not work in JP as well as the other way around.