“yiddish is better to learn in. I speak english yiddish and ivrit. You cannot come close in terms of clarity when saying a vort in english or ivrit.”
Toi,
My point about French was that for learning you like Yiddish the best, but that’s your preference based on your experience. If you want to talk about Rishonim and Aharonim, then you have to look at what they spoke. If they are your bellwether, then consider them as they were, not as you would like them to be. How do you know that Rashi would understand Yiddish? At that point in history, Yiddish was different, and clearly Rashi did not consider it lingua franca.