Answer:
vernacular
Step-by-step explanation:
Vernacular means proper of a place. Thus, it is possible to speak of a folklore, an architecture or a vernacular name. However, this word presents its true meaning in the context of linguistics, a discipline that scientifically studies languages.
The language of our personal and family environment is known as the mother tongue. Thus, a Japanese child living in Mexico will have a mother tongue, the Japanese learned in the family environment and, at the same time, a vernacular that is an informal language of the country itself. This child will learn Spanish at school and in their social environment.