Why user can't not get their own language(like big5)

In neomail > USER PREFERENCES FOR YOUR NAME

Language: No Big5 setting or Gb

But we can use ssh to edit their config file to tw(big5) or gb , and

in /var/cpanel/neomail/lang neomail have this language

cn de en fi hu ko no pt ru si tw
cz dk es fr it nl pl ro se sk


Any idea?