I think it would be necessary to add a parameter in the account of the user to indicate his native language.
This can be used for several cases
a) to connect and be in the right language (even if user have forgotten to choose the option at the login page).
b) for admin for example when creating an account or modifying it. So that it sends the mail in the good language of the user (and not in language of admin)
c) for notifications that the user defines on his file directories.
and we must certainly find other uses.
Customer support service by UserEcho