I've linked to Julien Chable's excellent French-language posts about Open XML many times, and now after spending some time in Spanish-speaking countries recently I have a couple of Spanish-language blogs to recommend as well ...
Chris Strevel of Intellekt has posted a bunch of Open XML content in Spanish on his blog. Check out his post "What Office Open XML means for developers." Chris leads a very progressive and fast-paced dev team at Intellekt in Mexico City, and he also happens to have won a Vista gadget contest earlier this spring.
Ricardo Jiminez has one of MSDN's most popular Spanish-language blogs at https://blogs.msdn.com/ricardoj, where he covers a wide variety of Microsoft technologies. I met Ricardo at our Open XML workshop in Mexico City last week, and he did a quick interview with me afterward that is now on his blog here. In Spanish, of course!
Do you know of any other non-English blogs covering Open XML? Let me know -- I'm planning to put together a comprehensive list of Open XML bloggers soon, and would love to include more blogs that are written in other languages.