I'm certain it is just a practical test if you are simply renewing a Greek licence at 74+, even if it came originally from a UK one, but I don't know what the requirements are for changing from UK to Greek at 74+.
As far as I am aware, but I could be wrong, the written test can only be taken in Greek. It is multiple choice so you don't need to write any Greek, just understand what the options mean. You might need to get some tuition from an English speaking driving instructor before taking it. I think that there are some oddities in Greek traffic law. For example a Danish friend was booked for failing to stop at a Stop sign. The sign was placed about 50 m before the junction so she did the obvious thing and stopped at the junction. The police claim she should have stopped at the sign, which would have served no purpose whatsoever. I looked at one of the trial tests in English and despite having driven here for over 20 years I couldn't always spot the correct option. Some are worded very strangely. Perhaps they were just bad translations.
PS You could try to contact the Ministry for Transport
and ask them if it is a requirement to take the written test. email@example.com