No idea but I tried to update my steering wheel to Stifflers mum new ones and messed things up big time.
I reverted back to my old steering wheel when it didn't work but all the digital numbers are all over the wheels and not in the correct parts of the wheel.
you need to have the english.uni and english.pos, those files need to go into your cars.wad and into your font folder in main gp4 folder! that are the language files and position files of the text!
yeah, seems to be a major prob. its very easy...so i wondering bout your problems. if you use my wheels, read the installation-readme carefully. install gp4 again and fresh (deinstallation necessary) then try it again, it should work if you copy the files german.uni, german.pos or/and english.uni, english.pos into the fonts folder.