Lingoes is Windows-only, but it could provide you a good, free translation solution.
Lingoes - super impressive dictionary and translation freeware
Lingoes. Lovely freeware dictionary and language translation program. Comes with a bunch of useful features like clipboard translate, right mouse click access for immediate translation/definition of any word or phrase, and the ability to download and install a large number of add-on dictionaries in different languages as well as English. Super [...]
(Via The Red Ferret Journal.)