Encoding of user ID strings

[Robert J. Hansen]

Is there any way to determine the encoding for a user ID string?

At first blush it appears the answer is "no, but most people use UTF-8."
 If so that's fine, but I'll have to silently discard a number of user
IDs that appear to be in foreign encodings or are garbled UTF-8.  I'd
prefer not to do this, so if there's some magic way of discovering the
intended encoding, I'd love to know about it.  :)