I have the task of re-designing a system to print shipping labels, using a networked Zebra GK420T. I have been able to send ZPL print jobs to it perfectly fine, but I cannot
Your "До свидания" were probably in cp1251. Encode it in actual UTF-8 and try again. Blank spaces are a good indicator that you have an encoding problem.
Verified with v56.17.112 firmware and ^A@N,,,E:TT0003M_.FNT