I remember reading about a German woman who after the end of WWII married one of the American soldiers and moved to the US with him. She then never needed to use German again until she was quite old. She barely spoke any German by that time. I think she was interviewed by a German journalist - that's why I ended up reading about it.
There were large swathes of Americans in those generations who stopped using German publicly because of World Wars One and Two. German was at the time the second most commonly spoken language at home in America. You still see vestiges of it in recorded data about ancestry [1].
I suspect many among them would've largely forgotten a functional knowledge of German by the ends of their lives, even though it was their mother tongue and kitchen table language growing up.
In the heart of Pennsylvania Dutch Country was a town that Bismark that changed its name to Quentin after Quentin Roosevelt died in the Great War (WW I).
I'm almost sure this was pre-Internet and paper. Asking Google is useless, I only get general pages about German "war brides". I'm trying to ask ChatGPT but right now it seems to hang while loading. I thought about asking DeepSeek, but I don't want to create a login (the ChatGPT site does not require one).
EDIT: ChatGPT actually loaded. I used the first paragraph of my comment as query. It did not give me a specific story, but it claims it "knows" about the phenomenon of German war brides forgetting much of their German, when they did not use it much after moving. Too bad I can't tell what the sources are for that information, ChatGPT saying something isn't proof.
