So the problem is actually that you feel excluded, not the language.
I'm going way off topic here for a second then I'll shut up, but gonna put this out there. You may want to think about this, since the language bothers you. It makes no sense that they're doing it to exclude English speaking people. What DOES make sense is one of two things.
1. The owner of a franchise speaks that language or a large portion of the population does, so using that language makes the restaurant run better if the employees use it among themselves.
2. Some restaurants, even very popular, well known ones, use illegal immigrants and student workers and trick them about wages and living conditions, then treat them like dirt and they're stuck and use them to run the business. They're stuck and they're afraid to say anything because of the possible consequences or students may not, especially at first, realize what's going on. Places like that need to get busted, but most people don't think twice about it happening at a big chain place and people don't think about poking around a bit and reporting anything odd.
Maybe befriending someone there and making sure the place is on the up and up and figuring out why would be both interesting and helpful, plus you'd be sure about the why of the language. I'm not sure why you feel it's to be excluded, but that must make you feel icky in some form - I hate to see someone feel bad/offended when the issue may be exactly opposite of what they're thinking.