If you want a more perfect translation tool than the UseKit mentioned above (or if you don't like the UseKit functions), give Side Tree Software's Translate a chance. This extension will connect with Google Translator to translate any text of the pages into 60 different languages (the default language is English).
Perhaps the best feature of Translate, adding a toolbar to Safari, is that it not only translates the text, but also converts the entire page containing the translated text and displays them into a new tab.