Yiddish exists in two groups of dialects, one of which is further subdivided. The western dialect, with few speakers, is centered in German-speaking areas of western Europe. The more widely distributed eastern group has a northeastern branch and a southern branch. The northeastern branch includes the Yiddish spoken in the Baltic countries and in the northwestern areas of Russia, and by Jewish immigrants or descendants from those areas. The southern branch-which has central and southeastern subgroups-includes the dialects spoken in Poland, Romania, and Ukraine.
Yiddish is a highly plastic and assimilative language, rich in idioms, and possessing remarkable freshness, pithiness, and pungency. Since it was spoken by ordinary people rather than by scholars, its vocabulary is weak in abstractions. By the same token it has few items descriptive of nature, with which the Jews of eastern Europe had relatively little contact, and a wealth of words and expressions descriptive of character and of relations among people. It makes liberal use of diminutives and terms of endearment and exhibits a variety of expletives. The use of proverbs and proverbial expressions is considerable. These qualities and usages give Yiddish a uniquely warm and personal flavor.
In the early years of the 20th century Yiddish was spoken by an estimated 11 million people living mainly in eastern Europe and the U.S. The use of the language has been declining since then. The initial cause was the extermination of the Jewish communities in Poland and other eastern European countries during World War II. An important factor that also contributed to the decline in usage was the adaptation by Jews to the languages predominant in the United States and in the Soviet Union. In 1984, however, a Russian-Yiddish dictionary containing essays on etymology and grammar was published in the USSR; since then a few novels by Russian Jews have been written in Yiddish. In Israel the Hebrew language is predominant, and Yiddish is a second language, cultivated largely by members of the older generation who have an eastern European background; only a few modern Israeli poets write in Yiddish. In an effort to ensure its preservation, the Hebrew University of Jerusalem teaches Yiddish, as do certain American schools and colleges. The YIVO Institute for Jewish Research, founded in Poland at the turn of the century and moved to New York City in 1940, includes the study of the development of the Yiddish language as part of its effort to preserve the history of Eastern European shtetl, or village, culture.