While you do not have to double major in Spanish, it is useful to be fluent in the language. There is a need for bilingual and ESL teachers, but also online content is growing substantially for Spanish speakers. Major news and information sites that are well-respected in the online community are creating Spanish outposts to reach an untapped demographic. Writers will be able to work in this field developing content, proofreading and editing, just as with English sites. While the rules and mechanics of Spanish is different, you are still utilizing your communication skills which flow naturally provided you are fluent in the language.