Simple Translate for Chrome, Opera, and other Web browsers which support Chrome addons. Works on Google Books. Unlike other free addons, this one doesn’t make you jump through hoops or go to Google Translate. It also has a feature that ensures it doesn’t work in places such as search-engine input boxes. Made in Japan, and a mature and maintained bit of software development.

How it works:

Select your target text, a small button shows up.

Click the button to instantly show the translation. Language is auto-detected.

While the translation box is displayed, you can also select and Ctrl + C to copy text from it if you wish.

Clicking away from the translation removes the translation box and also deselects the page text.

To run on Google Books, as seen above, after install in Opera:

1. Access Options. Run on all sites. (This appears to be the default, but make sure it is).

2. Applications. Manage Extension. Turn on “Allow Access to Search Results”, to have it work on Google and Google Books and other search results. Opera requires this, and I assume others Web browsers do also.

3. In its own Settings page there are also switches to ensure it does not display its button in unwanted places such as search-engine input boxes, password input forms etc. This vital feature is missing in a couple of other similar addons.