A well done, very useful program. Seems to have good support as well -- they responded promptly when I had a problem. Russian-oriented, since the program's developers appear to be Russian -- but there are dictionaries available that get you between English and a variety of other languages, and open-source dictionaries are also fully usable. I am personally using this program all the time.

My only criticism is that it is a bit unobvious how to install dictionaries. I figured it out (click on plus under dictionaries, and don't do anything else except click on the dictionary files you want to install) -- but some more guidance would be useful.

Now TranslateIt comes with a widget as well -- but don't judge the package by the widget, which looks very odd indeed. (Initially, I thought I was having some kind of video problem when I first saw it.) Additionally it does not seem to work reliably. So I just ignore the widget, and use the regular program instead -- which does not look odd and works perfectly.