It’s (all)Greek to

It’s (all)Greek to me(I don’t understand it at all)完全不懂,一窍不通
使用条件：We use this expression when we cannot understand something we read or hear.
当我们不理解看到的或听到的某件事时,可以使用这句表达.
This contract is written in such complicated language that it's all Greek to me.