High Quality Content by WIKIPEDIA articles! A first language (also native language, mother tongue, arterial language, or L1) is the language(s) a person has learned from birth or within the critical period, or that a person speaks the best and so is often the basis for sociolinguistic identity. In some countries, the terms native language or mother tongue refer to the language of one`s ethnic group rather than one`s first language. Sometimes, there can be more than one mother tongue, when the child`s parents speak different languages. Those children are usually called bilingual.