Yiddish is the language that klezmer musicians would have spoken. It started around the 1100s and is mainly early German, with some Hebrew and even local words, depending on the dialect. It is written using Hebrew letters, and reads from right to left. Star Trek's Mr Spock (Leonard Nimoy) speaks Yiddish! Many words had different spellings when they were written in Yiddish, and this carries through when they are translated into English. You can find some common variations on the dances page.
The Yiddish Language