Web content development by itself is already tricky and if needs to be done with a SEO approach, it becomes a multidisciplinary task. The team of professionals that embraces a multilingual content development endeavor needs to group skills in web writing and search engine optimization techniques in several languages. Some people think that writing in one language, running the content through SEO and then translating it suffices, but no.
SEO in Spanish is different than SEO in English, the structure of phrases and paragraphs is different and the use of keywords and keyword density is different in every language. You can start by writing in one language, then having the text professionally translated into the other language and then optimize each piece separate. Keyword analysis is also completely different, first because there are not many keyword tools in Spanish so the research involves using different techniques and tools and then correlating the results and then because the way a multi work key phrase is constructed in Spanish differs from English and it is not only a translation.
So if you are interested in content development for several languages make sure to ask for professional help that can assure you the multidisciplinary skills required for multilingual content development for SEO.