The iOS and Android apps are available in Spanish. The apps use the language settings specified in your phone's settings. If you change your phone to Spanish, the app will appear in Spanish.
Are other languages supported?
Not at this time, no. Currently, Spanish is the only supported language.
What about the docs?
All ZenDesk articles (such as the one you're reading now) have Spanish translations, which can be accessed by scrolling to the bottom of the webpage and clicking the 'English US' button. This will give you the option to transition into Spanish. The article that you're currently on, and any more that you open, will all be in Spanish.