"Click to translate" for .pdf

In my option for Windows the best option is QTranslate. Just select any word or text and double press CTRL.

QTranslate will automatically popup window with translation and additional info (depending on service you selected)

You can set input/output languages, translation service (google, yandex, etc...).

It has many other features and options.

And it's free!

And it's just 1 MB!

https://quest-app.appspot.com/home

The one extension I know work with chrome'spdf viewer is called reference.com dictionary lookup it will dd the extension and just select the text and then right click to translate it. From the store...

Simply adds an icon to the address bar and to the right click menu whenever you select text on a page. Clicking the icon or the menu item will open a new tab at reference.dictionary.com to show you the definition of the word(s) you have selected.

You can also try instant translate and see if it works for you.