The event can be whatever, it’s just the language code in the event URL that matters. Looks like the event pages themselves are not affected but your personal feed is.
Repro steps (repeat in this order, at your own peril):
This is still in English: The at Home Cycling & Running Virtual Training App
Maintenant en français : The at Home Cycling & Running Virtual Training App
Back to English, eh: The at Home Cycling & Running Virtual Training App