Diacritic
The Scandinavian languages treat the characters with diacritics ä, ö and å as new and separate letters of the alphabet, and sort them after z. Usually ä is sorted as equal to æ (ash) and ö is sorted as equal to ø (o-slash). Also, aa, when used as an alternative spelling to å, is sorted as such. Other letters modified by diacritics are treated as variants of the underlying letter, with the exception that ü is frequently sorted as y.