Internationalized string sorting

Has anyone done this?

Specifically, I have two strings, both UTF-8 encoded, and should have
at least the ISO-3166 country code and possibly the ISO-639 language
code.  How do I determine the lexicographical order of these two 
strings?

From what I can tell strcoll() doesn't work for this purpose as it 
assumes
a character encoding based on the locale string passed to setlocale().
The multibyte extension (mbstring) doesn't include any string sorting/
ordering functions, either.

-Bob