Click dictionary von newDev

This extension saves you time when reading text on a web page, in a foreign language, by allowing you to double click on the words you don't understand and providing you an intuitive translation popup.

Some of the supported languages, in no particular order, are: English, Spanish, German, Italian, French, Russian, Portuguese, Polish, Indonesian, Turkish, Hindi, Japanese, Chinese, Arabic, Korean and some more...

Chose between languages by clicking on the blue toolbar icon.
You can also disable the extension on a certain site, just navigate to that site, click on the extension and chose "Turn off for this page"