First language
A first language is the language that the person learned as the baby, normally from his/her mother. It is also known as the mother tongue.
Many people also have the second language, the language ay learned or started to use later in air life.
In some cultures, the person's language may more likely be that of his or her father. In this case it will be the "father tongue" rather than the "mother tongue". The mother will be likely to speak to the child in the language of his/her father. However, this can be very different from one group of people to the next.