When Android 6.0 was still in the developer preview phase, it was discovered that an update to the Google Translate app enabled in-app translation on devices running the Marshmallow preview. Now that Android 6.0 is rolling out to the public, Google has confirmed the feature.
If you have a device running Android 6.0 and the latest version of Google Translate, you can translate text from 90 languages in any app that uses Android’s text selection behavior. To use the in-app translation, simply highlight the text that you want to translate and then hit the Translate button that pops up. You’ll then get a pop-up box with the translation, and in fields that you can enter text, you can replace the typed text with the translated text with a Replace button.
This is a pretty big addition to Marshmallow. While you could accomplish the same thing by highlighting text, copying it, opening the Google Translate app, and pasting it in there, this new feature eliminates the need to launch Google Translate and lets you stay within the app that you’re currently using. That makes for a better, time-saving user experience.