I don’t particularly think that Yiddish is holy that being said I spent a summer living with my grandparents when I was a teen and I will say that I regret not having them teach me some yiddish.
They are secular but like most Jews of that generation in the USA they grew up speaking Yiddish at home and English at school (My grandfather also learned German, Latin and French)
The amazing thing is when a year or two ago a doctor asked him to write a sentence for some form of test he wrote out the first line of the Aenied, which he had learned in High School. He will be 99 this march!