Translation Service

Translation Service allows you to replace the selected text with a translation in any of several languages--in just one click.

It works in any Mac OS X program, so you don't have to copy and paste text back and forth.
Using Translation Service is simple. Select the text you would like to translate. From the application menu in the current application, choose Services > Translate > [language] --> [language]. The text will be translated in place. That's it!
Translation Service translates text between Chinese (Simplified), Chinese (Traditional), Dutch, English, French, German, Greek, Italian, Japanese, Korean, Pig Latin, Portuguese, Russian, and Spanish.
What's new in this version:
Improved the registration process.