You can translate the user interface of MailScanner Front-End. The WHM MSFE interface cannot be translated.
Take a copy of the file /usr/msfe/mslang.txt and name it mslang.cc.txt (replace cc with the correct country code of the language your users will be using). As an example you will see the file mslang.en.txt for the English version.
Translate the right side of each phrase pair to the appropriate language for that country code. The language file used will be based on the language selected in the user's cPanel.
The file mslang.txt will be overwritten when the mailscanner front-end is updated, so you should not modify that file.
The MailControl interface is not part of the language file so cannot be translated at this time.