Let me provide some more detail on what happened. I'm in the same area of the US I've been in for a while, and was driving one of the same routes I've driven frequently. In this case, fortunately, I knew where I was going, and only opened the route on maps in case there was a traffic problem for it to route me around.
Just after I started to exit the parking area, I drove by a Kia Sportage, and said something about it. I rarely use voice commands, but my Pixel 6 for some reason interpreted that as one, and an app I'm not familiar with opened and said "showing matching pictures," and displayed some pictures of Kia Sportages. I made some remark about not having asked Google to respond, and thought nothing more of it.
It was a few minutes after that when the maps app started giving voice directions that I realized it was in an unrecognized language. It doesn't sound like Spanish, or any other language I've heard before. I don't know whether the Sportage pictures and the language change are related, but often when two very unusual things happen back to back, they are related.
After finishing the trip, I started trying to troubleshoot it. I checked the main setting for language on the Pixel 6, and confirmed it is set to English. I found a setting for language within the maps app, and changed it from system default to English. It didn't seem like that would make any difference, but I have found with computers before that sometimes just making a change to something else that should give the same result works. It didn't in this case. I tried updating the maps app, but the unrecognized language in the vocal navigation instructions remained the same.
I then tried some voice questions to Google on the Pixel 6 without much luck. Finally, the one thing that sounded like it might have a chance to work was when it suggested a way to change voice instructions during navigation that was different than changing the system language or the app language. However, that method requires tapping on a profile photo or initial in the Google maps app to bring up a navigation menu, and I have no profile photo or initial in the app.
I am hoping I can get this fixed quickly, because I will soon be driving some routes I am not familiar with. I suppose I could try uninstalling Google maps and then downloading it and reinstalling it. I'd rather not, because in addition to not knowing if that would work, I don't know if that would delete all of my saved places, or if those are stored by Google and would be retained.