What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
To set the default language you should open your jotform and then click on the Languages option in the toolbar
When the window opens for languages you can set default and see what the default is. For your jotform I see that it is already set to Spanish.
Now your jotform is loading in English because not all strings (text) on your jotform is translated yet, only the header. My suggestion is to make all the translations that you might need and the jotform should load to you in Spanish once you go to it.
You can see more about the languages and how to use this feature when creating your jotforms here http://www.jotform.com/help/298-How-to-make-your-forms-multilingual
If you need any further assistance feel free to contact us back :)