We do indeed start the process of language-learning while still in our mother's womb. This tends to happen by about the fifth month of pregnancy. At this point in time our auditory systems are well enough developed to start this process. With our auditory systems developed we start to recognize our mother's voice. We recognize certain characteristics of it. That is pretty crazy. It gets even crazier. We can start to even recognize things like stories and songs that they have heard repeatedly.
Researchers found this out by testing newborn infants on their ability to make out and distinguish sounds. One of methods they use id referred to as the "high amplitude sucking procedure". It is a common behavior for newborn infants to suck, that's why we give them pacifiers. Sucking directly correlates to familiarity. Research shows that even at only two days of life, newborn infants suck more on a pacifier when they hear their mother's voice and native language. Even though it is at such an early age, newborns already prefer their mother's native language. It is an incredible thing that we do all of this so early on.