Answer to Question 1
All normal human infants are very similar in their capacity to perceive and respond to
language. Baby talk all over the world has similar characteristics because it reflects
language adaptations best suited for communication with infants.
Answer to Question 2
The possible explanations should include normal lag between comprehension and
articulation, as well as severe problems in hearing and/or mental development, with
several explanations in between, such as the possibility that the child does not hear
enough language spoken to him or her. Further, you may comfort your friend by
pointing out that using and understanding any form of communication is more
important than language usage, per se.