This sure was an interesting first JavaScript project. It turned out harder than I expected, but I've learnt a lot, from JavaScript/jQuery basics to free dictionary APIs and JSONP format.

Obviously, there is still work to be done, but this is a basic functional bookmarklet. The goal will be to fix some bugs to enable it on as many websites as possible. Also, there are many ways to expand this (translation, more dictionaires, ...), but it obviously depends on available free APIs.

I'd love to hear some feedback from you (especially on speed, compatibility and user-friendliness)!