Yiddish was at one time the international language of Ashkenazic Jews from Central and Eastern Europe and their descendants. A hybrid of Hebrew and medieval German, Yiddish takes about three-quarters of its vocabulary from German, but borrows word liberally from Hebrew and many other languages from the many lands where Ashkenazic Jews have lived.
It is generally believed that Yiddish became a language of its own some time between 900 and 100 C.E. Yiddish was primarily a spoken language rather than a written language.
It has a grammatical structure all its own and is written in an alphabet based on Hebrew characters. Scholars and universities have classified Yiddish as a Germanic language.
Yiddish was never part of Sephardic Jewish culture - the culture of the Jews of Spain, Portugal, the Balkans, North Africa and the Middle East. They had their own international language known as Ladino or Judesmo, which is a hybrid of medieval Spanish and Hebrew much in the same way that Yiddish combines German and Hebrew.
At its height, less than a century ago, Yiddish was understood by an estimated 11 million of the world’s 18 million Jews, and many of them spoke Yiddish as their primary language. But Yiddish has fallen on hard times, a victim of both assimilation and murder. Today, less than a quarter of a million people in the United States speak Yiddish, about half of them in New York.
Yiddish is referred to as “mame loshn”, which mean “mother tongue”. Mame loshn was the language of women and children, to be contrasted with loshn koydesh, the holy tongue of Hebrew that was studied only by men.
The word “Yiddish” is the Yiddish word for “Jewish”, so it is technically correct to refer to the Yiddish language as “Jewish”.