locale errors

[Ashley Graham <ph33rful@optonline.net>]

how do I fix this:

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

I can't remember what I did, but this error wasn't around the whole 
time. I think it started appearing after I installed something, but for 
the life of me, can't remember what.

It's popping up when I try to run some programs, and causing certain 
ones to stop/crash, and other's to run "fine".