At this time we do not have a Korean language pack but this only translates the SmarterMail interface and does not affect sending emails.  If the emails have ????? then the sender will want to change the text encoding to UTF-8.  To do this have the users go to Settings | Account Settings | Compose tab.  Then the emails should appear in the correct language. 

 

You can translate the SmarterMail interface.  Here is a link that will help get you started.

I am glad to hear that resolved the issue.  If you want to push this to all your users in the domain login as the domain admin and go to Settings | Domain Settings | Advance Settings | Default User Settings | Compose tab and make the change.  After that is done all future users will have the UTF-8 setting.  To push it to all existing users in the domain go to Settings | Domain Settings | Advance Settings | User Propagation | Compose Tab and check the Text Encoding box and then Propagate Now button.