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.