Looking at lisp/textmodes/ispell.el, there are a number of regular
expressions such as this one taken from the "german8" entry of
ispell-dictionary-alist-4:

[a-zA-Z\304\326\334\344\366\337\374]

The last seven numeric character codes in the above are the iso-8859-1
(ISO Latin-1) encodings for letters used in German that are not
encoded by ASCII.  If your mail reader can handle UTF-8, the
characters represented by these iso-8859-1 codes look like this:

[a-zA-ZÄÖÜäößü]

My question is: are emacs regex character classes limited to the
iso-8859-1 character set, or is there some way to represent Unicode
(such as UTF-8) characters in a character class?

Thanks,

Chip

-- 
Charles M. "Chip" Coldwell
Senior Software Engineer
Red Hat, Inc
978-392-2426