Bret is spot on. Open data would unlock a vast amount of wealth. Other suggestions: A collection of various kinds of texts, translated into 20-30 different languages. 100 million words (per language) would be fine. 20 minutes of text, spoken in thousands of different voices/accents.
An open translation dictionary is a fantastic idea. You would have to be careful to clarify the context. A word in one language can often translate to several words in another language, for example. But I think it's do-able. And I think you meant 100 thousand words per language. :-)
As for dictionaries, there's wiktionary, but it's broken because it's based on words, not meanings, so you'd need 30*29 translations for each word.
Mmm, maybe I should do it...