Currently Being ModeratedFeb 20, 2013 5:06 AM (in response to Ilgiz valiev)
Many login systems will only handle plain text, and you should stick to that - upper or lower case letters, and numerals - no odd punctuation characters or diacriticals.
Currently Being ModeratedFeb 20, 2013 6:30 AM (in response to Roger Wilmut1)
Digest autification send information in UTF-8.
When I analyze packages with WireShark I see that for example Windows WebDAV sends this text in UTF-8 encoding, and all characters were sended correctly regardless of language.
iCal just doesn't send Authorization header if characters no in ASCII (0-127).