If you do a lookup for an artist name which contains characters which are part of latin-1 (e.g. the names Müller, Fernández, Sørensen will get plenty of results), they display as broken characters (diamonds, boxes or question marks depending on your browser), other non-ascii characters outside the latin-1 range work fine.

This seems to be because the json is returned as latin-1 instead of utf-8, with other characters escaped - http://test.musicbrainz.org/ajax/search?type=artist&query=M%C3%BCller&offset=0&limit=8