Unfortunately Korean cannot be added at this time due to some problems. I will attempt to fix these problems but a Korean translation will not be available any time soon, Sorry to give this bad news.
Viewing post in Cartridge 2 has been released! comments
It is due to issues with displaying the text not translation, It will take more time for me to understand and find a solution so that all text in all supported languages can be displayed correctly in the game, unfortunately at the moment attempting to add support for Korean characters breaks support for Chinese and Japanese.