Is there a library of recordings of the German dialects spoken east of the Oder-Neisse line before 1945 available on-line?
I guess if you click your way through youtube you are going to find some old recordings.
Here is something from Nazi German time I found. Apparently some German ethnologists went out to all areas of Germany, Austria, Danzig and the Czech Lands in years from 1935 to 1937 and recorded the German dialects they heard there.
The result was something like a jukebox called "Lautdenkmal reichsdeutscher Mundarten" (Sound Monument of Reich German Dialects). They wanted to devote their efforts to the "Führer" but to their misfortune Hitler hated dialects. He wanted to be the people he considered as German to be as uniform as possible. So he disencouraged the whole project and the "Sound Monument" was forgotten in an archive in Marburg.
It was rediscovered in the 1970s and today it is a valuable source of spoken German dialects how they were spoken just two years before the horrors of WWII began that destroyed old Europe and many of its dialects.
Here the link: uni-marburg.de/~naeser/ld00.htm
For Low Prussian dialects (spoken from Danzig/Gdansk to Memel/Klaipeda please click on:
13. Danzig / Gdansk
18. Elbing / Elbląg
24. Angerburg / Węgorzewo
26. Stallupönen / Nesterow
68. Tilsit / Sovetsk
For German Silesian dialects please click on:
48. Ober Hermsdorf/A village close to present day Nysa
4. Baberhäuser-Hirschberg / Jelenia Góra
There are many old German dialects there to discover.
Please don't bother if you speak German but nevertheless hardly understand anything. Even I have a hard time understanding them. Since all of these dialects are close to extinction the 21st century German ear for dialects has forgotten about those ones. But its a good way to grasp the sound of the dialects