I live in Finland where they have two native languages: Finnish & Swedish. In a lot of places you'll see both the Finnish & Swedish place name on road signs. Without getting into politics, it's a good assumption to assume that Finnish is the mother-tongue of most of the population - with some areas having Swedish as their native language but also perfectly capable of speaking Finnish fluently.
I have my phone's language set to English as a native English speaker. Google maps reads me the Swedish road signs, in English.
I live in Ontario where major highway road signs are bilingual, e.g. “427 North/Nord”. Google has ingested these, blindly translates the French part, and tells me to take “427 North North”.
Fwiw, you can set (on Android at least) the language of Google Maps independently of the rest of the system. I also have my phone set to English, but maps set to Dutch because otherwise the reading out of street names can be incomprehensible compared to their proper pronunciation.
This does mean your navigation instructions are also in that language, which may or may not be a problem, depending on your fluency (but there's not really a whole lot of phrases to learn.)
Yes I discovered this, this weekend. As you mention, that relies on it being your native language. But it's absurd that if I'm in driving in a foreign country it would attempt to read the names of the streets in your own language's dialect.
Maps is so annoying for that: I travel to France, Italy and Germany on the road, and language is set to English on the phone, so it tries to pronounce everything the English way, and I can’t understand anything.
I wish I could set a "read location/road names in local language" setting.
It's worse in Taiwan where road signs are in both Chinese and Pinyin (romanized chinese) and Google Maps will randomly shown you only one of them for turn instructions. Good luck recognizing some obscure character for a town name in time if you are not fluent in Chinese. I would be surprised if this hasn't caused any accidents.
I have my phone's language set to English as a native English speaker. Google maps reads me the Swedish road signs, in English.