I will give a crash-introduction on the Yiddish language, while standing on one foot. I may do Yiddish a grave injustice, but in my innocence I would claim that it is a kind of German intermixed with Hebrew and Slavic words, written in Hebrew script, being primarily the spoken language of the huge Jewish communities mainly in Eastern Europe. The Nazis of course changed all that. But for more history, etc. check out the Wikipedia entry on the subject.
Concerning the linguistic part of Yiddish I have the following to say: The German originated words are spelled extremely phonetically. While the Hebrew words are not. They are spelled in one way, pronounced in another. Though there may be a certain logic to it that I haven’t discovered yet. So this is why the Hebrew phrase “Shalom alechem” is pronounced differently in Yiddish: Sholem aleychem. And it’s not the only one. To come up with more examples: Hebrew “chatunA” (wedding) with stress on the latter part of the word is pronounced “CHAsene” in Yiddish. Or “yishar koach” (well done!) becomes “shkoyach”, “yom tov” (holiday) becomes “yonteff”, “Torah” (the Pentateuch) becomes “Toyre”… And so on. The spelling is the same. The pronounciation different.
Now, the German part of Yiddish is also confusing for those familiar to the German language. Like myself. Not very familiar, but quite a bissl – a bit. Let’s pick a random word – big. Gross in German – groys in Yiddish. Nicht (not) in German – nisht in Yiddish. Sagen (say) in German – zogn in Yiddish. Laufen (run) – loyfn. Fahren (travel) – forn. Antworten (answer) – entfern. There is a tendency to use more gutturals. Like in “ich”. The German pronounciation is soft. The Yiddish is hard – like in CHUtzpa.
Let’s take the children rhyme: “Ich hob a tatn mit a mamen, ich hob a shvesterl, a kleyne. Mir zeynen ale fir tzuzamen, a mishpochele, a sheyne.” Translation: “I have a dad and a mom, I have a (little) sister, a small one. We are all four together, a family, a beautiful (one).” If you know German you may imagine the meaning. Except from “mishpoche”, which is from Hebrew – “mishpacha” (family).