I have talked to many people in French without realizing they can't understand me. This cracks Jim up. He, thankfully, knows enough Spanish to make himself understood and translate for me.
Today is our first Spanish lesson; I'm on break right now. Spanish is similar enough to French to make it recognizable, but not similar enough to make it easy. In fact I have spent the last two hours confusing French and Spanish, and I expect the next week (at least) will be more of the same. At least now people will understand me--hopefully!