Spanish isn't my first language, but I grew up with Mexican neighbors, took 2.5 years of it in college (5 years worth), and got really immersed into the culture. During my 8 years of playing FFXI and playing FFXIV 1.0 on and off since CE release, I met a lot people who spoke Spanish and had lead Spanish-speaking linkshells. Not everyone spoke both Spanish and English, some just Spanish. They were some of the most devoted/dedicated people I'd ever met, tackling content, adapting from our mistakes, and enduring the length of hardship till we finally got the prize. The game's clients at the moment are only in Japanese, English, French, and German, considering these are most likely the countries in which SE offices/studios are and the languages they learn to do international business. International business has expanded, however, to include a lot more languages. Almost every product I see out there now has multiple languages on them.
In the future, (though it can be said about any language/country) SE should consider expanding this game's client/forums/support services to the Spanish-speaking world in particular, seeing how it is a primary language in a vast number of countries, and a secondary to some. It is an emerging universal language and kids these days start learning foreign languages as early as elementary (English, French, Spanish, German, and in some cases, Japanese) because..well this article can explain it better http://www.early-advantage.com/Articles/topten.aspx.
Also, catering a client to this population would make it more enjoyable for Spanish-speakers due to being able to understand what the content is about, especially since not all of them are bilingual. How much it would cost to implement, for resources, staff, and management, I don't know, but these are just my thoughts. They've been cutting down on their staff as of late, but should they get to a point where they are afloat again, this may be an idea to look into.