This is a great idea. Seems like it could a pretty effective way to learn a new language. I've installed it and it provides a pretty good options panel where you can customize the frequency of translated works and the color of the text. It would be nice to have a tooltip for the translated words which displays them prior to translation. This would eliminate all guesswork and be slicker than turning the extension off and on again.
If you rollover the translated words it seems to give you the original meaning, although it would be better with the surrounding context I guess. I've already filled a bug report as it seems to be translating proper nouns and numbers as well :)
Ah yes I see it takes the original values and sets it as an alt attribute. The fact that I didn't realize it initially may speak to a UX issue. Might be worthwhile to have the original word show up a little bit sooner.
