[Typo3] Problem with ä, ö etc. special characters in image menus

[tapio]

I have a huge problem with image-based menus with ä, ö, å - they don't 
work with normal way. Presumably depending on server definitions, which 
I can't do anything. 

I tested a plugin (addgfxheaderce), which makes graphic headers and I
added these lines into it in order to get scandinavian characters
printed:

 $text= str_replace('Ä','Ä', $text);
 $text= str_replace('Å','Å', $text);
 $text= str_replace('Ö','Ö', $text);
 $text= str_replace('ä','ä', $text);
 $text= str_replace('å','å', $text);
 $text= str_replace('ö','ö', $text);

In the list above:

Ä = & + # 196 + ;
Å = & + # 197 + ;
Ö = & + # 214 + ;
ä = & + # 228 + ;
å = & + # 229 + ;
ö = & + # 246 + ;

I should make corresponding changes to the core file class.tslib_menu.
php for gmenu menu type ( jus for this menu type - not for other menu
types).

I tried to find the correct place to change and I tested in many places
but I didn't get the change.