From my understanding, the Jewish European languages, including Yiddish and Ladino (judeo-spanish) have a short of frozen in time quality.
I know more about Ladino because I know Spanish and am always interested in romance languages. Many (though by no means all) of the differences between that and modern Castilian are that Ladino has not kept current with Spanish phonetic changes from the 1500s onwards. I believe I've also read Yiddish has a similar quality of seeming, from a distance, like it has some characteristics that might have been seen among German speaking gentiles in prior times.
I think that when you see separations of populations, you sometimes see the preservation of "archaic" language features.
Luther was a major force on the standardization of (school) German, wasn't he? It makes sense to me that his influence would have bypassed Yiddish. I take it to be mostly a variant of old regional German. I base this on transcriptions to the Latin alphabet that I have seen, for I have never learned the Hebrew alphabet.
Archaic language features: I have heard that Quebecois French was some centuries behind what is spoken in France.
I know more about Ladino because I know Spanish and am always interested in romance languages. Many (though by no means all) of the differences between that and modern Castilian are that Ladino has not kept current with Spanish phonetic changes from the 1500s onwards. I believe I've also read Yiddish has a similar quality of seeming, from a distance, like it has some characteristics that might have been seen among German speaking gentiles in prior times.
I think that when you see separations of populations, you sometimes see the preservation of "archaic" language features.