How to identify an Imam (A.S.)?

Humairi narrates in his book “Qurb al Asnad” that Abu Naseer once went to Imam Musa al-Kadhim (as) and asked him, “How to identify an Imam?” The Imam (as) replied, “the first characteristic of an Imam is that he must have been nominated by his father to succeed him as a mark of Itmam al-Hujjat, or fulfilling his duty. This is the same way as the Prophet (S) had nominated Amir’ul-Mu’mineen ‘Ali (as) as his Vicegerent or Imam. The other characteristic of an Imam is that he is able to give answer to any question that is asked of him, and has the faculty to give the reply to a question before it is asked.The Imam can answer the question in the language of the questioner.”
Then the Imam (as) said, “Be seated that I give you the Proof of my Imamat.” At that time a Persian, from Khorasan, came there and asked a question in the Arabic language. The Imam replied him in Persian, the man’s mother tongue. The Khorasani said, “O Holy Imam! I had put my question in the Arabic language thinking that you might not know Persian! But you speak better Persian than me!” The Imam (as) told to the man, “If I cannot reply you in your language, then you become superior to me; but then, how could I be your Imam if I don’t know your language?” Then the Imam (as) said, “O Abu Muhammad! The language of no person is strange to the Imam. He knows the tongues of the animals, birds and all the living creatures. The Imam can be identified and recognized with these characteristics. If a person claims to be an Imam and doesn’t have these manisfestaions, then he is not an Imam.”