Complex language/ethnicity question. I know in the area East and Northeast of Plzen (blue circle) there is a significant population with German-originating surnames (Müller, Böhm, etc). Up to the beginning of the 1800s, many parish records there were recorded in German, but only briefly later they switch to Czech and never switch back. Of almost all the people I’ve found who immigrated to America from this place (ie Rokycany/Beroun), their graves are recorded in Czech (if not English) and never German (even those with German surnames) so that implies almost all people there from the latter part of the century mainly spoke Czech.

The area to the left, poorly scratched in red, was from what I can tell majority German and German-speaking (ie Sudetenland before WWII). What I’m wondering is were the people in the blue circle “initially” Germans who became “more Czech” when more Czech people migrated in with their language in the 1800s, or was this area “initially” Czech where Germans moved in (significantly enough to garner German priests) and gradually assimilated to Czech?

I feel like this question can apply to a lot of places, like Prague or Sudetenland. Was Prague & Sudetenland in medieval times actually “German”, or was it Czech to then become majority German, then going back to Czech after WWII? Or maybe this is just a “chicken and the egg” thing.