Korean-holidays is simple package for Emacs calender.
If you use MELPA, just do:
M-x package-install [RET] korean-holidays [RET]
If you want to use ‘korean-holidays’ exclusively, add below to your init.el .
(setq calendar-holidays korean-holidays)
If you want to use ‘korean-holidays’ additionally, add below to your init.el .
(setq calendar-holidays (append calendar-holidays korean-holidays))