mSlovnik is the best double-sided multilingual dictionary for Mac OS. Translates without an Internet connection into 4 languages: English, German, French and Spanish.
Integrates Bing Translator Service via which enables the translation of whole sentences, or words not in the database. This feature, however, requires an Internet connection. Such translations can be found save for later off-line use..
InstantTranslate makes it really easy to translate a selection of text in the application you are working in from one language to another language.
One World Dictionary by Ascendo is a leading multilingual reference tool for Apple desktops.
