Not passing message['language'] to _user_mail_text()

in user_import.inc's implementation of hook_mail(), the message language is not being passed to _user_mail_text() - instead NULL is passed.

ie:
_user_mail_text('register_admin_created_subject', NULL, $params)
instead of
_user_mail_text('register_admin_created_subject', $message['language'], $params)

Not sure why, but it makes sending emails in the user preferred language impossible.

Attached patch applies against 6.x-2.x.