Many applications for OS X are available in different languages. You can change your system language, including all program languages via System Preferences –> Language & Text (requires a user log-out). Language Switcher, however, can change the language of any single application of your choice (if the software comes in different languages, of course). Simply select the program and choose from the available languages. Language Switcher will restart the app in the desired language and lets you specify a default setting too.