How to deal with customers?

I work at a makeup counter and I have an awesome counter manager, we get along great and work together well. Shes Hispanic and speaks english and Spanish which is very helpful since we’re in a very mixed area. All different races and cultures live here, so often there’s a language barrier and she’s able to communicate with the customers and translate for the other coworkers.

So we have some regulars and when they hear my coworker speaking Spanish they call it “obnoxious” “deplorable” they complain to our head manager and want to get her fired because of it! They say such awful things and I just ignore it and continue with the transaction. It still just makes me mad to hear them, I don’t know what I could do. Is there an appropriate way to tell them to stop?