Steins;Gate. It starts slow, but once it picks up it’s amazing and puts all that slow build up to good use. Not sure if it technically counts though. Visual novels are a weird middle ground that aren’t really book or game, but there are some really good ones. Definitely the way to go if you’re in more of a reading mood but want some art and music to go with it.
I don’t have a source handy, but from what I remember: yes, a feral child can learn language later, but never to the same level of fluency. It’s more like learning a second language. Also there is extremely limited data because it mostly comes from horrifically abusive situations.
If I remember right, the most interesting data came from a study that gathered deaf children from areas where they had no sign language. The young children rapidly developed sign language, but the older children (teens) had a hard time keeping up and did not reach the same fluency.