Was the Development of Yiddish Primarily due to Intermarriage or Rather (Linguistic) Assimilation? How Long did it Take the Settling Jews to Switch from a Romance (a la Ladino) to the Germanic Yiddish?
The development of Yiddish is very hotly debated. There are multiple theories of where it developed. Tablet Magazine had a two part series on it a while ago that you might be interested in: