I haven't seen Bangkok Dangerous, so correct me if I'm wrong, but isn't Chakrit's character Thai, so it would make sense that he would speak with a Thai accent. Why would some random Thai guy speak English with an American accent, you wouldn't except a Italian, French, Japanese, etc character to speak with an American accent, would you? If I was playing Thai character that hasn't live abroad, is of mix ancestry, or anything that would enable me to speak English fluently, I would play the character with an accent.