if you can't find the Greek language to the phone, it means that the device wasn't meant to be sold in your country.
the only option you have is to go to a Nokia Care point and ask them to install the Greek language pack for you, there might be a fee.
note that after reinstalling the same firmware or updating to a new one, the language will be lost and you should visit Nokia Care again for the same procedure.
i suppose you live in Patra?
agiou nikolaou 56
t.k. 26221
tel. 2611103556
Greece Nokia X6 RM-559 v32.0.002