The phrase "native tongue" refers to the language that someone learns and speaks from birth, typically the language spoken in their country or culture. Full definition
It's a dead language in that it hasn't been anybody's native tongue for over a thousand years. (bookbrowse.com)
Since we each speak a different native tongue, a lot gets lost in the translation. (penguinrandomhouse.com)
Embrace of the Serpent is a film whose dialogue is delivered primarily in native tongues but eight other languages factor in as well. (digitalshortbread.com)