Google Translate for Android works systemwide in Marshmallow
The Google Translate app for Android has a new trick up its sleeve, but for now it only works if you're running the Marshmallow Developer Preview. This will, however, become more widely available as the final release of Android 6.0 Marshmallow gets out and starts spreading.
We're talking about the fact that Google Translate works systemwide, if you run the aforementioned iteration of Android and also if you have version 4.3 of the app (or newer).
As portrayed in the screenshots above, what this means is that when you select some text in whichever app you happen to be using, you don't have to copy it, then switch to the Google Translate app in order to have it converted into another language. Now when you select text "Translate" appears as a direct option, and if you tap on that a pop-up Google Translate window will show up and quickly give you what you want.
This functionality takes advantage of Marshmallow's new contextual selection feature, and it should work anywhere you can select text. This makes using Google Translate on Android for things you find written in an app or on a website a lot more useful than it's been so far.