Well, when in Rome. English is spoken by most people in the United States who conduct business, and if you want to do business, speak English. I remember this diner I went to with a waitress who barely spoke any. She confused orders, got me the wrong one, then billed me for the original (which was more expensive). It's just business sense to learn english and have your employees speak it, but if the situation calls for it (like if your diner is in the middle of Spanish Harlem) then learn spanish for the sake of your business.