Idiom translation is one hardest translation-related tasks. Idioms cannot be translated literally, as it will result in non-sense. In order to translate an idiom one should find the equivalent expression in the second language. It requires deep familiarity with the language and knowing the specifics of its metaphorical speech. WikIdioms is in fact a multilingual dictionary of idioms, created by native language speakers.
You can find a lot of Greek idioms translated to English and vice versa.