Translate Text is an application for Mac OS X that provides services you can use to translate short passages of text between different human languages.
Translation is performed by Google's AJAX Language API. This means that translation requires a connection to the Internet to work, since the translation does not happen on your machine. It also means that the language selection is subject to that API's limitations, and that I cannot guarantee the app will always work.
One World Dictionary by Ascendo is a leading multilingual reference tool for Apple desktops.
InstantTranslate makes it really easy to translate a selection of text in the application you are working in from one language to another language.
