It helps very much to be able to speak the language in whichever countries you're in.

Although I may not be fluent in all of them, I try to be as conversant in as many as possible.

Perhaps the language factor encourages the taxi drivers to think, "Hey, maybe this guy isn't as dumb as he looks, or knows this place a little better than I thought..."

Likewise, just being able to say "Hello, how is business today?," in the local language does a lot to break the ice, possibly to strike a conversation leading to great suggestions on local places that would ordinarily have gone unnoticed.