In this video a teenager with a British accent asks Alexa to "Turn on the floodlights". It understand. Then he asks it "Turn off the floodlights" and it doesn't understand. He tries again but with his best effort at an American accent, and it understands him.

Then, I come on and do a comically bad American Southern accent. I even say "Turn off them floodlights" and it understand. Note: this Alexa is set to British English. You can hear the accent when it speaks.