Speak English or what...??

Okay, I have a lot of Spanish speaking employees. That is becoming normal in restaurants around here. Therer are a couple of girls in particular that actually are some of my best service people--friendly, quick, clean, accurate--the english they know was learned mostly on the job. Of course, I get complaints now and then because their accents are hard to understand if you don't pay attention. I understand that will happen. I try to be sensitive and helpful. One complaint I got recently was this..exact words:
"Why don't you be hiring more english people? These ('deese') people be takin all our jobs away! McDonald's be goin out--you be racialism. I don't got time for this ('dis') kind places. Tell them ('dem') peoples to learn english or..or.."(cell phone rang, she left).
I smiled and said "good morning" to my next customer.

I am wondering if maybe..just maybe..immigrants can't learn english because we don't speak english. Whose english is correct? England's, America's, Philly's, West Virginia's........_________?