I run php ../../tests/parserTests.php --file=citeParserTests.txt in extensions/Cite.

All the tests pass except "<ref> with custom group link", which includes custom numbers in Klingon ("wa' cha' wej loS vagh jav Soch chorgh Hut wa'maH"). I get the following result:

-<p>Wikipedia rocks!<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[wa']</a></sup>
+<p>Wikipedia rocks!<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[klingon 1]</a></sup>

When I just try it on a usual wiki page on the same wiki, it works as expected.

It may be a problem with the way that I run the tests, but I cannot think of anything (but I'm really not a Parser tests expert either.)