OP has another post on the definition of heritability, which I really liked: https://dynomight.net/heritable/

> For example, if you tell me what language your parents natively speak I can tell you your primary language with >90% accuracy.

According to the link above, the heritability of the primary language is zero, whereas the heritability of what language(s) a person speaks in general (whether primary or secondary) is not necessarily zero and varies by language.