Русско-англо-русский юридический словарь

Mother tongue and Native language have similar, meanings and are often actually interchangeable, however there is a subtle difference.

Native language refers to the language of the area the person grows up in. For example, growing up in the United States, your native language would be English. It's the language used every day everywhere you go by the vast majority of the people there.

Mother tongue refers to the language of the family you grew up in. The language your parents spoke in the house, or to each other out-and-about if applicable. Often, parents will use the same language as that of the region (parents in the U.S. speaking English) however it can differ. Take for example a family of immigrants from Mexico to the United States. In their house and with family/friends they may use Spanish. But at school, restaurants, stores, etc they would use English. In this case, the native language is English and the mother tongue is Spanish.

Typically, the two will refer to the same language, in which case they are interchangeable; however, in some cases they may differ. (StackExchange)

As a widower himself, he decides to ask Laura out when he meets her at school and tells everyone what a perfect date they shared. (Daily Express)

The application of absence tiers by schools will help to reinforce the importance of regular attendance at school. (BBC News)

Campbell will later tell BBC Radio 5 Live: "I was badly beaten up at school by a teacher who was a leading light in the Scripture Union." (The Guardian)