Is Yiddish really a language? Or is it a dialect of German? And does anyone speak it anymore?
The quick answers are yes, no, and yes, respectively. It used to be a dialect of German—12 centuries ago—but both languages have changed so much in the intervening centuries that they are now separate (but recognizably related) languages. A bit like, say, French and Spanish. Yiddish has primarily been affected by an admixture of borrowings from English, Hebrew, and other languages, but many words are still easily recognizable by those who know German. I mention French and Spanish because I’ve never learned any Spanish, but I can still predict a lot of words by knowing the sound correspondences from Latin and from French.
A linguistic word before we go anything further: language is speech, not writing, which is merely a representation of speech. When you compare two languages, you may need to use writing as evidence, especially in a textual medium like this one, but we’re still talking about speaking! Writing often tends to be archaic and not a very accurate representation of the language.
With that in mind, the question of the day is whether German and Yiddish speakers can understand each other. I have to tell you that I was a bit surprised at the answer. The fragmentary Yiddish that I grew up hearing matched very well with the German that I subsequently learned, and I didn’t pay attention to (or wasn’t aware of) all the differences. Check out this highly informative video in which a German speaker and a Yiddish speaker attempt to understand each other—but be aware that both languages have regional differences, so that the speech of a German speaker from Munich will not be exactly the same as one from Hamburg, and a Yiddish speaker whose family is originally from Lithuania will not be exactly the same as one whose family is originally from Belarus.