Locale annoying warning

["Pedro I. Sanchez" <pedro.i.sanchez@altavista.net>]

Hello,

I have a fresh unstable install and every time I operate on the packages 
with apt-get I get the following:

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

Where am I supposed to set these variables, /etc/profile? Where am I 
getting this lower case "c" from?

Thank you,

--
Pedro