A couple of postscripts:
1. I spoke to someone who read through Rav Dovid Cohen’s book on Yiddish. It was originally a part of a larger work of drashos and aggadah. It’s not meant as a psak. One example he brings is the pejorative “shlemiel”. Rav Dovid cohen says it’s from Shloomiel ben Tzurishaddai, the one nasi who can’t have his korbon laining during chanukah fall out on shabbos. So if you call someone a shlemiel, are you yotzei Talmud torah, or are you violating mechaneh sheim lechaveiro? And are you yotzei learning if you have no kavvanah for it?
Rabbi Blech says it’s called Mamalashon because the tatteloshon was loshon hakodesh- the Men spoke Hebrew, the women spoke Yiddish or Judeo-German.
I still am waiting for the Mekor of the Chassam Sofer, because Reb Moshe does to disagree.