Very often, as I'm listening to an article being read by an American English voice with swipe-down "Speak Screen" or selected-text "Speak Selection." A date or number would be spelled in Dutch by the Dutch voice, or a name in French by the French voice, which would often prompt that voice to take over and continue reading to me the English text with the same enthusiasm, even if the words make absolutely no sense: It's just English with a terrible French or Dutch accent.
I haven't found a way to turn this autonomous language switch off. I looked in Accessibility -> Speech and Accessibility -> VoiceOver to no avail. There hasn't been a single time in which said feature was useful, I don't read multi-languages text, or see why a date or a number should be spelled in Dutch. I don't speak or use either language.