Linux Visual Novel Reader (LiViNo Reader) provides a live translation of Japanese words rendered within a game, simply by mouse-hovering them.
It works by combining:
LiViNo Reader will live-stream all the text rendered by the game directly to the Rikaichan dictionary so you can get an instant translation by just hovering a word.
For detailed instructions about installation or usage, please check the LiViNo Reader page.
Some games confirmed to be working are listed on the wiki.