Transmiti lets you run your desktop documents through Google Translate
Just download the standalone .EXE, run it, and Transmiti heads to your system tray. Highlight some text in a Word or OpenOffice Writer document, tap the hotkey, and your translation appears in a movable popup. It's still Google Translate doing the heavy lifting, so the results are generally good -- though you may get the occasional Python-esque "I will not buy this tobacconists, it is scratched."
Now, here's my only gripe with Transmiti. For some reason, the Windows key is the hotkey and there's no way to specify your own combination. Transmiti only kicks in when you have highlighted text and press Win, but still -- I use that key a lot, and it would only rarely be used for translations. It also won't jump in if you use combinations like Win+R or Win+E.
Transmiti is already a very good desktop translation app, so hopefully the developer will add a customizable hotkey option.