Dovid, forget it. Antisemitic websites are full of English translations along with “commentary”. Anyway, I have it on the authority of the wife of a friend who is from Switzerland that someone who knows Swiss-German can understand Yiddish.
Yiddishekop, I am quite certain that the Ben Ish hai did not give shiurim in Yiddish and I know that Rav Ovadia did not. Rav Soloveichik switched to English at some point when he realized that talmidim were not understanding him. I could go on and on but I have other things to do.