Make sure, you are doing this in "Google Chrome". [THIS WILL NOT WORK WITH OTHER BROWSERS]
Go to projectnaptha.com and add the extension to your Chrome. Voila!
Once installed you can select the text and Copy, Translate and.. wait for it.. Replace the text!
Step 1: Copy
Step 2: Translate (it uses Google Translate for this, fair enough)
Step 3: Replace (Select text->Right click->Translate->Modify Text)
There you Go....
