Whats yiddish?

Yiddish is a mix between Hebrew and German used by the Jews in Europe. It is quite old and there was a time when for almost 1000 years it was the only language some of the Jews spoke. It flourished until the 1920's and since then it declined. today it is becoming and "endangered" language as less and less people know and teach it. 

Here you can get some details about the history of Yiddish 

Yiddish (ייִדיש yidish or אידיש idish, literally: "Jewish") is a non-territorial Germanic language, spoken throughout the world and written with the Hebrew alphabet. It originated in the Ashkenazi culture that developed from about the 10th century in the Rhineland, and then spread to central and eastern Europe, and eventually to other continents. In the earliest surviving references to it, the language is called לשון ־ אַשכּנז (loshn-ashkenaz = "language of Ashkenaz") and טײַטש (taytsh, a variant of tiutsch, the contemporary name for the language otherwise spoken in the region of origin, now called Middle High German; compare the modern New High German or Deutsch). In common usage, the language is called מאַמע־לשון (mame-loshn = "mother tongue"), distinguishing it from biblical Hebrew and Aramaic which are collectively termed לשון־קודש (loshn-koydesh = "holy tongue"). The term Yiddish did not become the most frequently used designation in the literature of the language until the 18th century. For a significant portion of its history it was the primary spoken language of the Ashkenazi Jews and once spanned a broad range of dialects from "Western Yiddish" to three major groups within "Eastern Yiddish". Eastern and Western Yiddish are most markedly distinguished by the extensive inclusion of words of Slavic origin in the Eastern dialects. While Western Yiddish has few remaining speakers, Eastern dialects remain in wide use.

The general history and status of the Yiddish language are discussed below, with further detail provided in a series of separate articles on:

• Yiddish dialects – as spoken in different regions of Europe
• Yiddish morphology – the structural detail of the language
• Yiddish orthography – the written representation of the language
• Yiddish phonology – the elements of the spoken language

Hi, 

As mentioned by my fellow knowledgeable friends Yiddish was at one time the international language of Ashkenazi Jews. This was the case in Central and Eastern Europe till the middle of the 20th century. The interesting thing about Yiddish is that it's a hybrid language. It's comprised of around 75 percent German and the rest is borrowed from Hebrew and all sorts of other languages.

Today there is still research being conducted in many universities regarding the history of the Yiddish language and Yiddish literature.

Here is a site that gives a very interesting outline of the language. Enjoy, and best regards.