Word Lens is a free download on the App Store, but the two currently available dictionaries--Spanish/English and English/Spanish--cost $5 each. The app only works on iDevices with video cameras, which should be obvious given its augmented reality nature. Because Word Lens is primarily a word-to-word translation system, it’s not going to retain the nuances of grammar or sentence structure. But it’ll get the idea across.
With more languages likely to come in the future from developer Quest Visual, Word Lens and Google’s Text-to-Voice ambitions may revolutionize international travel and communication within the next few years. So long as you have a smart phone, anyway.