It doesn’t matter how you say “huh?” as long as you say it. If you don’t understand something, please do not just smile and nod. The person with the impairment/accent knows you’re just BSing them, and nobody is fooled. People do this often with me and while I know they’re just trying to be “polite,” it makes it frustrating as hell when you know you’re not being heard.
It’s easy in New York. We smile and point and say ‘2 blocks that way, and make a left’.