Why are some people unfamiliar of their own language?

It depends on your family and how much time and effort they are willing to put into you to learn the language. How much time they spend at home, and what language they use to speak to you. It can also depend on the individual as well. If an individual is really motivated to learn a language (especially at a young age) he or she can. When I was little my grandparents would speak Yiddish all the time and I really wanted to know what they were saying. I spent so much time around them (spying hehehe) that I learned the language. We speak Russian at home. I decided to teach myself the alphabet and how to read. It wasn't easy, but now I think I've finally got it.