There are any number of problems that can be caused by a language barrier, up to and including lost sales.
But Spanish and English aside, based on what you said, it sounds like the customer may have had an attitude. He could have been having a bad day and was taking it out on you. Or it could have been frustration over his inability to get his point across to you. I wouldn’t take it personally, because how could it be personal? If he had just walked into the store, he couldn’t possibly know you.
Regardless, the ability to serve customers in their native tongue is good business and opens doors to more revenue. It sounds like your store is in a good position because it already employs someone who speaks Spanish. I would leverage that as much as possible. People feel more comfortable when they can conduct business in their own language.