vernacular (adj.)
c. 1600, “native to a place”
from Latin vernaculus “domestic, native, indigenous
from verna “a slave born in the house rather than abroad” a word of Etruscan origin.

Used in English in the sense of Latin vernacula vocabula, in reference to language.

As a noun, “native speech or language of a place,” from 1706.
So:
–(of language) native to a place (opposed to literary).
–expressed or written in the native language of a place, as literary works: a vernacular poem.
–the language or vocabulary peculiar to a class or profession

As in ‘the Tri-Cities’, ‘the back forty’, ‘the Inland Empire’, or ‘Appalachia’.