The ability of children to acquire language is not generally dependent on race, social class, geography, or intelligence. At some point the ability to acquire language decreases.
Adults can learn additional languages given sufficient opportunity.
Adults learn in different ways than children. By imitating speech a subject is more easily learned than by study and books. You can see this in my little daughter. Although she is not four years old, she knows how to speak well and, indeed, clearly, about household matters. He was to teach them the language and literature of the Babylonians.