Yiddish is just one more way to give the impression that someone or a group of people are holier than thou. It’s only an illusion of frumkeit. It’s not real.
BS”D
It is a way of preserving the Torah based culture of the communities that once existed in Europe and had to rebuild in the US or EY.
It should be preserved as it clearly has Jewish roots. Only the Chassidic communities are doing much to preserve it as a language fit for speaking Torah and living Torah lives.