I answer my own question.
To change the interface language to English, you need to go to the Machine parameters menu from the main menu (photo 1), go to item 6 (photo 2), enter the password (photo 3, in my case it is 1603, look for it in the documentation for the machine), using the F1-F4 keys go to item 189, use the F5 key to change from AUS to EIN.
Press F7 to exit. That's it, now you have English (photo 6).
P.S. I really liked this machine, despite the fact that it was made in 1996
I am very happy for your post about ZK850. I have a same machine, I bought 2 years ago but didn't use it. Unfortunately I haven't got any expirience with this machine. I am using AGIE and Deckel for cavity EDM and Fanuc for wire. I will try the change of language because I don't speach german.
Unfortunately the machine don't begin, it forgetted the system parameter. I have some floppy with system files but the floppy driver can not read anything......I will suffer continue.............