Our brain is fascinating. Imagine the power of our mind if we can learn many languages... Tsss incredible just that!

If you have a strong memory, the same thing also happened in your family when you were a few months old. How did it happen that you know how to speak and write ? Don't underestimate primates' capabilities where a complex psychic and sensory system come into play.

Motivation, business purposes, to be eager to learn....

I don;t have an answer for you, partly because I am not sure what motivates your question, but I do know that in my town there is a class to learn sign language run by a deaf lady, who does not speak. She has designed a course where you start from nothing & build understanding. So, I suspect that it is possible. Some argue that children are born with an innate grammar that is configured when they are young to the language(s) they hear, but they also seem to learn starting with no common language.