The world is not all English, not even on the Internet. In the US the Hispanic population is growing and has become an interesting market if approached correctly. Spanish is the first language of Mexico, Central America, South America (except Brazil), much of the Caribbean and Spain and the first and second language of more than 40 million Hispanics in the US.
A list of search terms or keywords that people might use to find your website in different languages must be developed. This is not a simple matter of translating your English keywords. People might be using three terms in English, where only one exists in Spanish. Most ideas in English need 15% more words to be correctly expressed in Spanish. And a page often has to be optimized for multiple variants of a word in each language so the task becomes time consuming and can only be well executed by a team of experienced optimizers with Multilanguage skills. The other consideration is that a good SEO campaign must be accompanied with a content development strategy and that also needs to be done in two languages
If you are engaging into a search engine optimization campaign, be sure to consider the Hispanic market and do it already in English and Spanish. Multilingual SEO can really help your business reach new leads and new markets.