Historically speaking, english always was the second language in that part of the country…
Ninety-nine percent of the time I’ve found that everyone there speaks english better than the average suburban teenager and will usually greet you with a cheerful "Hello!" after speaking rapid-fire spanish to the residents who came in right before you… just enjoy it like you would a if traveling in a foreign land.
As for where to eat… oddly enough I’ve never had much luck in Brownsville, but right up the freeway in McAllen there’s three places I love… Taco Palenque, Casa Del Taco and Shipley Donuts. All three are around the same area in McAllen (10th Street) and are an easy Google search to find.
Taco Palenque has a really great selection of grilled meats and a fantastic salsa bar that features probably 10 different fresh salsas, fresh chopped cilantro and onions, pickled vegetables and peppers of various heat. The Casa Del Taco has great carne asada tacos and choriqueso (a hot plate from the oven with a brick of melted cheese in the center, topped with chorizo… cut it with a knife and roll it into fresh tortillas… Mother of God it’s good). Shipley Donuts I think may be a chain, at least in the state of Texas, but the one on 10th Street in McAllen just feels like a mom-and-pop place… the donuts are pretty damn spectacular, too.