That's a tough one, because you really need both options available.

"Mispronouncing" to your phone's language is actually helpful if you don't speak the language, because you'll legitimately understand it better. Local pronunciation can often be completely and maddeningly unrecognizable to a foreigner.

While if you speak the language, it's obviously nonsensical to have it mispronounced and you want the real thing of course.

Example: "Rio Tinto" in Portuguese is pronounced "HEE-oo CHEEN-too". If you don't speak the language, you're NEVER gonna map those sounds to a street sign because the "r" and "t" sounds you're expecting aren't there at all! While hearing a completely incorrect "REE-oh TIN-toh", you can probably recognize.