The learning starts in the womb, even before birth. There is research evidence for this. But it depends on how one defines learning. Recognizing the mothers voice is something the infant learns early. And there are several hundred things that are learnt in the first few months. Please do not try and teach the baby a specific fact. Be affectionate, respond to the baby's needs and play with the baby in appropriate ways. Even a bell tied to the crib is a learning tool. Singing the baby to sleep is good. You would not have to worry about teaching unlearning to the child. Children observe, connect things and learn to anticipate events even in their first few months.
It is natural for parents to use the mother tongue in talking to the baby. Whatever they speak will become the language, the child will learn. There is no specific disadvantage in the use of any language. Children easily pick up 2 or 3 languages, when they hear them spoken in the home and community.