Cultural relevancy is key. We’ve all gotten a few laughs out of improper translations, or ones that are obviously written by a non-native speaker. A professional translator should be a native Spanish-speaker for this reason.
More people are reading in Spanish, and Amazon is catering to this audience by encouraging self-published authors to enter the 2nd annual Indie Literary Prize contest. Translating books from English to Spanish now has even more opportunity, as more Spanish-speaking readers turn to Amazon Tienda Kindle for Spanish books.