Hi,
İf you want to change debian’s system language you must follow these steps;

sudo apt-get update
sudo apt-get install debconf
sudo dpkg-reconfigure locales

Or you could add something like the following lines to /etc/environment

LANG=”en_US.UTF-8″
LANGUAGE=”en_US:en”

If you want different locales for different users, you can add that to their
.bashrc files

Here’s some links that touch on what you’re looking for:

http://gallery.menalto.com/wiki/Debian_locale_HowTo

http://melkor.dnp.fmph.uniba.sk/~garabik/debian-utf8/howto.html