My phone is and has always been set to English (system language).
Some days ago, after the latest update, it started speaking in tongues: First thing I noticed is that one of the buttons in the upper drawer had somehow switched to French (the rest of the phone was still in English!).
Slowly, over the next days, more and more parts switched to French, till I got tired of this nonsense and rebooted: Everything went back to English…
So, FYI, if parts of your phone suddenly start talking in Hausa or Maori, know that the solution is to reboot.
For the record, yesterday I was in Settings/System, and noticed some menus were in French again. But only seconds later, while I was watching them, they switched back to English: “Oops, sorry, we didn’t mean to!”
.
Seriously now, if somebody ever decides to investigate this issue (I won’t hold my breath), it seems that since one of the last updates the OS eventually decides to switch to one of the SIM’s language, in my case Orange FR (although it could had chosen Vodafone DE too), but there is a safeguard mechanism that overrides this initiative with the system language chosen by the user. Mechanism which eventually fails, and the phone start switching language, bit by bit.
What I fail to understand is by which mechanism the OS decides arbitrarily to progressively start changing the system language bit by bit. I could understand everything changing at once, but individual menu items?