Many thanks for your help Jochen, did learned a lot.
I stumbled to a problem, the spoken & txt lanuage change for a MKIV is totaly clear for me, but didnt found a good know-how for changing them both on a MKIII. Using TweakNav i can edit the TXT-fields for the MKIII file but i understand that renaming the voice files for a MKIII does not work.

There are a few MK3xxxx voice files on the ISO (not even a NL/DUTCH) file in there i think also strange,only GB,DE and more)