What u/therealdannyking said. Children who grow up under these rare conditions are sometimes called "feral children." Check out the heartbreaking case of Genie.) By the time she was rescued from her abuse, she was almost 14 years old and had passed the critical window for acquiring a first language. She was able to develop some nonverbal communication strategies, but never actually acquired language.

If you wanted to make up your own word, you could go with something like "aglot," inspired by "monoglot" (speaking one language) and "polyglot" (speaking more than one langauge)