original: A first language (also mother tongue, native language, arterial language, or L1) is the language a human being learns from birth.
simplifications: A first language is the language a human being learns from birth. A native language is the language one learns from birth. A first language is the language a human being learns from birth. It is also called a mother tongue, native language, arterial language, or L1. A first language is the language a human learns from birth. It is also called mother tongue, native language, arterial language, or L1. A first language  is also called mother tongue, native language, arterial language, or L1. It is the language a human learns from birth. A first language which is also the mother tongue or native language is the language a person learns from birth. A first language is the language a human learns from birth. A first language is the language a human being learns from birth. A first language is the language a human being learns from birth. It is also known as mother tongue, native language, arterial language or L1. A first language is also known as mother tongue, native language, arterial language, or L1. It is the language a human being learns from birth.