Everytime I start perl it complains "perl: warning: setting locale failed"

Does anybody have an idea how to set LANG, LANGUAGE, LC_ALL, LC_CTYPE in my /etc/environment or any other config file (debian potato) or where to find docs?

I played around with different combinations of de, de_AT, de_AT@euro ... (according to debian euro manual) but none seemed to work out right.

I'd be glad to have ANY valid setting (no matter if german german/austrian or english)