If you need to change character set to en_US.utf8 or ko_KR.utf8 on CentOS 7, you can change it by localectl r changing locale.conf. Please take a look belows

Change by localectl

# localectl set-locale LANG=ko_KR.utf8


Change by modifying /etc/locale.conf

/etc/locale.conf
LANG=ko_KR.utf8