It is too difficult to use because it does not support Korean language.
Support for viewing and writing that members can see at least in the Forum.
감사합니다
What do you mean exactly?
The software can be translated to almost any language, and it does support almost any character set you can come up with.
There isn't a Korean language pack I think, but if you want one - you can even help create one SMF is searching for translators! (https://www.simplemachines.org/community/index.php?topic=552016.0) :)