special characters in url rewrite

[Majora]

Hello,
I would like to have a URL like this: http://www.rechnungswesenforum.de/threads/537903-umsatzsteuernachberechnung-fuer-das-vorjahr

URL's are lowercase and special characters are rewritten in the case ? becomes ae.

I've tried to set this:

public static function cleanURL ($ fragment)
{
$ Translite_simbols = array (
'?' => 'U',
'?' => 'u',
'?' => 'A',
'?' => 'a',
'?' => 'ss',
'?' => 'o',
'?' => 'O',
'?' => 'c',
'?' => 'C',
'?' => 'g',
'?' => 'g',
'?' => 'u',
'?' => 'u',
'?' => 's',
'?' => 'S',
'?' => 'i',
'?' => 'I',
'?' => 'r',
'?' => 'c',
'?' => 'E',
'Ue' => 'u',
'Oe' => 'o'

);

in the public static function clean_entities ($ fragment) function
Unfortunately, this with vBulletin 4.2.1 Patch Level 1 does not work.

What's wrong?

Best regards
Matthias

[Majora]

Anyone?