How to solve error when enabling mysql in ubuntu 18.04 - perl: warning: Setting locale failed

i am running this command to enable mysql service:
systemctl enable mysql
but, it issues an error:
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = (unset),
iam using ubuntu 18.04 LTS here. In this video i will show you how to solve that error. See video for detail.