Yiddish is mainly a mixture of what two languages?

Yiddish is the historical language of the Ashkenazi Jews. It originated during the 9th century in Central Europe, providing the nascent Ashkenazi community with a High German-based vernacular fused with elements taken from Hebrew and Aramaic as well as from Slavic languages and traces of Romance languages. Yiddish is written with a fully vocalized alphabet based on the Hebrew alphabet.

Prior to the Holocaust, there were over 10 million speakers of Yiddish; 85% of the approximately 6 million Jews who died in the Holocaust were Yiddish speakers, leading to a massive decline in the use of the language. Assimilation following World War II further decreased the use of Yiddish both among survivors and Yiddish-speakers from other countries (such as in the Americas). However, the number of speakers is increasing in global Hasidic communities.