If you are a professional translator using a Mac, you may be interested in tools for CAT (Computer Assisted Translation). One of these is a specialized word processor that makes provision for keeping source and target text carefully organized and has a "translation memory" to automatically help the translator use earlier work to process new text. Two such applications for OS X users are AppleTrans and OmegaT. An excellent survey of the field can be found at the Wikipedia CAT page.
One important area for translation work is the localization of OS X applications, i.e. providing the means for the menus and dialogues of a program to be displayed in the user's native language. For this special tools are required to extract and replace the parts of the application containing the texts. Apple provides the programs AppleGlot and ADViewer for this purpose. There are also 3rd-party alternatives including LocFactoryEditor, iLocalize, and Localization Suite.