Not on staff of SpanishDict.com, I cannot of course answer your question... Hey! wouldn't it be terrific if there is a published API to the several dictionaries you reach on the dictionary page. I have used the hardcover versions of both Velasquez and Chambers Harrap. They're great. I, too, would welcome such an API...or one to reach the RAE.
But I also have the problem of not always having access to the Internet:-( That second problem is more than the frustration of waiting for a web page to load. As I said I've purchased old fashioned dictionaries to use when not online.
Then by chance I ran across an older digital edition of one of my dictionaries in a small strip-mall computer shop -- for very little money...about..oh..maybe it was $19..
It is called iFinger. When deciding to respond to your post, I looked to see if they are online. And they are...I found that they have a Spanish-English dictionary that sits on the desktop for $31. I also found a freeware popup dictionary at popdict.com.
I kind of doubt that you'll get a positive response to your query...But these might be alternatives...and less work. Someone already wrote the program provides you with the interface.
I do not know if they have a developer api for translations, but I have seen spanishdict.com "widgets" you can include on your own website. I think that is more along the lines of "word of the day" though, not translation...
Translation services are provided by Google, Yahoo, and some other engine whose name I can't recall right now. Google seems to have the best results for me...maybe Google has an API, but I don't know.