I'm not disagreeing with your suggestion that a mechanism would be needed to set the "preferred accent/dialect" for a listener. My point is that when I was referring to accented English, I was referring to people for whom English is not their native language, for example a native French speaker. I know that people speak English in different ways in different countries, and that there isn't one "correct" English. But I was referring to people who speak English with a foreign-language accent in particular, who are the most difficult for me to understand at high speed.