To perform a translation of text from within an app, simply highlight the text you want translated, choose which language you would like it translated to, and that’s it. Once selected, the text will then be translated in a pop up window via the Translate app.
As noted in Google’s post, this feature should work in most applications once updated, unless the developer created a custom text selection behavior. If that’s the case, this feature will not work and the developer will need to implement the standard Android text selection behavior.
The update is rolling out now to Google Play, so be sure to grab it if you are in fact running Android 6.0 on your device.
Check out Google’s GIFs below to see it in action.