I've used this setup with Ubuntu, Mint, and Crunchbang.
Change the Danish dk to the Greek 2-letters.
Go to etc/default/keyboard and make changes that fix your situation:
The last line is what I've found very easy to use to toggle between languages.
I use my left little finger to touch both shift and control keys together.
Wirth's law - Software is getting slower more rapidly than hardware becomes faster.