Yiddishe Loshen
Yiddish Language is a strange creature. When Jews fleeing the crusades migrated from France and Italy to Eastern Europe, their Hebrew began mixing with the native Germanic and Russian languages of the areas into which they settled. Y iddish evolved as a spoken language first, and a written one much later. Since so many different Jews in so many different areas speak so many different versions of Yiddish, up until recently there was no "official" orthography.
Jewish scholars like Alexander Harkavy and Uriel Weinreich have at last, in the past century and a half, tried to codify Yiddish. The information I present here refers to this "official" Yiddish language, but Yiddish you encounter may be quite different, especially in the realms of pronunciation and idioms.