I don't think AI will be able to fully grasp the intricacies of human language until it has "lived" long enough to form the links between ideas and experiences. Mainly in the physical realm, as obviously a lot of our human development is shaped by our environments. They will need eyes, ears, and maybe noses. We should also consider giving them subconscious or instinctive reactions to certain stimuli. An AI wouldn't immediately know that, for example, rotten meat is bad to humans because it lacks a nose to send a signal of danger and disgust.
We should also consider the idea to communicate with AI in regular face-to-face speech. Talking is not the same as writing, and conveys a lot of information beyond just the words.