A way which I frequently use to defuse that sort of objection is "Many people speak with accents [+], but that typically means they speak another entire languag

A way which I frequently use to defuse that sort of objection is "Many people speak with accents [+], but that typically means they speak another entire language, so try to be a charitable listener." A blunter way of putting it is "I will accept any criticisms of Dr. Yamada's English ability if you're capable of articulating them in Japanese." or "How's your Japanese?", both of which I've had regrettable need to use in professional contexts before. [+] Fellow linguists will know this is an abuse of jargon but it's the easiest way to communicate the concept to someone who isn't a linguist.