Comment 3 for bug 1205713

I am also affected by this; using Ubuntu 13.10 with en_US.UTF-8 locale, and unable to type Greek.

Can you see at all the Greek localisation of Unity in 13.10; A Russian translator mentioned that the Russian translation is not visible either. A quick explanation would be if Unity runs under the C locale, which is not a Unicode locale.
If the only characters that can be typed are from ASCII (http://www.asciitable.com/ - NOT extended), then most probably it is a locale issue not supporting the UTF-8 encoding.