(As an apt parallel, albeit perhaps obscure to many here, saying Yiddish is not dead because the Haredim use it is like saying that Sogdian is not dead because it survives as Yaghnobi. But the Yaghnobi language used by some impoverished people in an isolated valley is a pale shadow of the cosmopolitan Sogdian language that was used before.)
Talk to a linguist if you want the very messy and complex details I just summarized to the point of butchering the truth.
This is an amazing piece of information, even more incredible it is the fact the modern speakers can read Nietzsche with no problem at all, what a fantastic coincidence.
I mean, what native German speaker could even begin to understand this Schiller poem, it is 200! years old!! It could be very well be written in proto-Germanic:
An den Frühling
Willkommen, schöner Jüngling!
Du Wonne der Natur!
Mit deinem Blumenkörbchen
Willkommen auf der Flur!
Denkst auch noch an mein Mädchen?
Ei, Lieber, denke doch!
Dort liebte mich das Mädchen
Und’s Mädchen liebt mich noch!
Willkommen, schöner Jüngling!
Du Wonne der Natur!
Mit deinem Blumenkörbchen
Willkommen auf der Flur!
In practice natives had trouble understanding each other if they traveled just a few villages over
How do you mean that? Of course there were different styles of speaking (especially in polite speech), but it‘s perfectly intelligible either way. In fact, even Martin Luther‘s German still sounds colloquial today (although the spelling was vastly different).
> English of today is close enough to English back to around 1500
That‘s a hundred years before Shakespeare. Who is decently understandable with some practice, but not what I would call „close“ to modern English.
I don't know much about Yiddish but I believe it's in the former category. Yiddish was by far the most common language among Jews who were murdered in the Holocaust; there are still fewer than 10% as many Yiddish speakers in the world today as there were in 1930. But according to Wikipedia "the number of Yiddish-speakers is increasing in Hasidic communities."