Positively but it's not really going to make you that unique. There are many of us applying who can speak 2+ languages. It's a great thing to add, though, esp. if you have strong connections to the related culture (i.e., can relate to them well, etc., and, therefore, later be a resource in medicine). I'd suspect simply knowing enough Spanish to get by in Mexico is probably a bit more "meh," but if you're fluent enough to be a medical interpreter and have sufficient cultural immersion, this is certainly something of some value that might be brought up in interviews.