Language learning belongs in the child's domain. Language is something we all learned as kids without a lot of thought or stress. It just seemed to happen. Adults, on the other hand, struggle with learning another language. Granted, for some it comes fairly easy, but for most of us who go abroad, it's one of the hardest things we'll ever do.
Language is something everyone creates.
Everyone constructs his own version of the language. N one speaks it exactly like another person. Those who already speak it are models, but language is not precise, like math. Language is dynamic. Since they haven't completely locked in to that sound system, they are able to accommodate another one.