the.com/vernacular

means The everyday, informal language native to a particular place, people, or group, as opposed to formal or literary speech.

from From Latin 'vernaculus,' meaning domestic, native, or home-born — itself rooted in 'verna,' a slave born in the master's house rather than bought from outside. So the word's oldest sense is about belonging to the household by birth, not by import; it later widened to mean anything native to a place, and by extension the home-grown speech of ordinary people rather than the imported, 'proper' language of scholars and officials.