In order to fix the german-shell in Kanotix (close cousin of knoppix) one does this:

first off, go to (as root) /etc/locale.gen file and remove all the lines not of your desired language (saves time later - assuming you want to keep en_US ISO-8859-1) and save that file.

Then, apt-get install localepurge. Localepurge's config will come up during the install and see only the language you have in your locale.gen.

Then, another trick. you need to run as root again the command localepurge

For editing the file, if you are more comfortable not in a shell, you can do ALT+F2 then type kdesu konqueror and give root password. Browse to the locale.gen file in the etc folder and when you doubleclick it kwrite or another editor will come up.