Freelang offers a Free Offline Dictionary Program. Install the program once, then download as many word lists as you need. On the English version of Freelang, the program is in English and all word lists use English as source/target language. You can browse the word lists, add your own words or create your own dictionary. Many languages are available, and updates are frequently uploaded on our site, thanks to the contribution of our users.
85 dictionaries are now available on the English website. The program was downloaded 1,230,000 times in year 2006 in total (all websites).
New (July 2007): it's also possible to search the dictionaries online (no download needed).