in Eastern Europe, these people ('native Germans'

did (and, as far as they have not fled, been forcefully expelled, killed or absorbed during or after the war, some of their anchestors - albeit a small number compared to the early 1940s, still continue to do today) speak German, sometimes a particular dialect brought in by their anchestors that had immigrated to these countries typically several 100 years back. Depending on the particular country (and its policy towards this 'national minority'

there were towns with German names, German-language schools, church-services, universities, and so on.
Alsace is a bit different in this respect that historically speaking it had been an area of 'Germanic' people (if you allow for this rough division, as opposed to 'Romanic' people of more Western Europe). The Alsacian language as part of the Aleman dialects (maybe a different term would be more appropriate linguistically?) makes, again linguistially speaking, part of the family of German dialects. Historically the French rulers, both kings and republics, have steadily pushed their boundaries east in the quest of expanding their territory, and after the late middle ages more and more of Alsace came under French control (which of course cluded that over time, i.e. centuries, more and more people of French origin moved there as well and that the French culture including language was more and more adopted by the locals). By 1940 most Alsacians would probably have agreed that they were 'French' (anyone from that particular region might be able to give a more detailed insight).