You need to go back to where you obtained the Korean folder icons and download them again. Then you can replace the missing folder icons by overlaying. I had to do the same thing with a folder icon I was missing. (Not a Korean one though.)
Every time you create a new folder, it will use the default system icon. You have to overlay the system icons each time with ones that you wish. You can no longer install a program that will overlay all icons (folders and apps) since Lion. That's why the popular app "Candy Bar" was released as free ware because it doesn't work.