Hello, Maksim, There are 2 set phrases: "mother tongue" and "native language". They both refer to the language one has started learning from birth. But they are not identical: when using "native" the reference is more to the country/nation, when using "mother" the reference is to the parent (mother or father). The word "tongue" means also "a fleshy movable muscular part of the floor of the mouth". If you need more information about these words, write me and I will explain it in more detail.