Ok - i never do. Dont seem polite to me to ask everytime.
But thats me i think. I learned to go carefull with strangers. Its easy to harm or upset people from other cultures.
But i just met a very dark man today at the office. We talked some and he turned out to be a computer programmer from Ghana. And he could some danish. But dosent matter. We always talk english here anyway course of all the mixed people from everywhere.