I have a character who was kidnapped from his family at age four and has spent the last twelve years of his life locked in a basement where he was routinely abused and neglected, and not really spoken to beyond a few short orders. He's been rescued and placed back with his birth family and a whole team of therapists and psychiatrists/psychologists. Before he was kidnapped, he was a vibrant, chatty child and was probably a little ahead of his age group in language acquisition, but not at a genius level or anything.
What I want to know is: how much language should he have now and how much should he be able to acquire? It's kind of complicated since I know the brain goes through its second culling at five, thus ending the critical language acquisition period. However, would he lose what language he had learned at that time? And, if so, about how much? Furthermore, how much should his sixteen-year-old self be able to get back? Full speech seems unlikely, but perhaps coherency and short sentences?This takes place in modern day, by the way.
Research Done: Googled "feral children", read everything I could find on "Genie", Googled "language acquisition + abuse" and found lots of information I already knew. Called upon my (somewhat rusty) memory of Early Childhood Development and psychology. Browsed through little_details but didn't find anything much.
Any advice would be much appreciated, thanks!