Debian - How to fix Perl warning about locales

When I restarted the lighttpd service, the console raised this warning:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = (unset),
LC_CTYPE = "UTF-8",
LANG = "en_GB.UTF-8"
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

It is because the locales settings of the system was not configured properly. So, to fix this, run the following command:

# dpkg-reconfigure locales

And choose the correct locale file, in my case, it is "en_US.UTF-8".