Yiddish dialects are variants of the Yiddish language and are divided according to the region in Europe where each developed its distinctiveness. Northeastern "Litvish" Yiddish was dominant in 20th century Yiddish culture and academia, while Southern dialects of Yiddish are now the most commonly spoken, preserved by many Hasidic communities. The principal differences between the dialects are found in the quality of stressed vowels, for instance Litvish zogn, Polish zugn 'to say'.
Read more about Yiddish Dialects: Varieties, Comparison, Development of "neutral" Form, Standardization Controversy, Documentation