title: How to fix a locale setting warning from Perl
body: <p>When I run <code>perl</code>, I get the warning:</p>
  
  <pre>perl: warning: Setting locale failed.
  perl: warning: Please check that your locale settings:
      LANGUAGE = (unset),
      LC_ALL = (unset),
      LANG = "en_US.UTF-8"
  are supported and installed on your system.
  perl: warning: Falling back to the standard locale ("C").</pre>
  
  <p>How do I fix it?</p>