You can read about the translation (in Greek) here:
Εξελληνισμός των WordPress 2.8 και Thematic 0.9
And see the Greek Thematic live here:
The translation was in general easy and a pleasure, but I run into a couple of problems:
1. The string “Thematic Options” is not translatable.
2. text-transform:uppercase is not appropriate for Greek (because its output violates the rules of Greek orthography). So, users of the Greek translation will have to use Thematic with a child theme, to override the text-transform rules of the parent.