You don't have to, if you don't want to. Or you're experiencing something you did not mention in the question? I'm guessing you mean although your system is set to English, the websites you visit offer you just Spanish? Do they have the ability to provide English content if it was preferred at all? Search engines oftentimes do not honor language setting, but use geography for their defaults. You might wanna go through [[Choose display languages for multilingual web pages]] in case your content preferences are not what you'd like them to be.