If you run see this when running Perl it’s because OS X Terminal.app sets LC_CTYPE to “UTF-8” when it should be a locale string like the others. Set it to en_US.UTF-8 to fix it.
perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = "en_US:en", LC_ALL = (unset), LC_CTYPE = "UTF-8", LANG = "en_US.UTF-8" are supported and installed on your system. perl: warning: Falling back to the standard locale ("C"). locale: Cannot set LC_CTYPE to default locale: No such file or directory locale: Cannot set LC_ALL to default locale: No such file or directory