The best answer would be for GOOGLE TO PLEASE FIX IT so we can have an option to turn street name speaking on or off regardless of the chosen system language and the chosen Google Maps spoken language (they should be functionally separate).
However, this is the only current work-around I have been able to discover:
the solution is simply to change your entire phone language to the foreign language you want spoken, as apparently the street names can only be spoken in the phone's default language. This is dumb.
Anyway: main phone settings --> System --> Languages & input --> Languages --> Add a language --> choose the one you want (ex: French) --> tap and hold the hamburger icon (3 horizontal bars) next to this new language and drag it up to re-order this language to be on the very top (it is now your default system language).
That's it! Now, back in your Google Maps navigation settings you'll see that the default language (French) is now chosen, and under it it says what it used to say for the English default language: "Prononce les noms de rues" (Speak street names). It now speaks street names in French, just like it used to do for English. However, the down-side is that my entire phone is now in French instead of just the audio for my Google Maps, like I wanted. Google, please fix this!