Three or four times over the years, a fav blurted has out something in perfect English, zero accent. I was astonished but didn't call her out at those times.
Recently, I asked her to drop the fake accent for just 30 minutes. She gave a perplexed look but refused to break character - or even speak. Busted.
Overall, these ladies are wonderful actresses. Yes, some overdo it and some genuinely have limited English but the rest...well, it's their bread and butter. I guess we should be grateful for the fantasy.