At least in recent versions of Android there is that OCR (?) powered functionality to select text when you're in switch-app view.
I would suggest that these days you'd be much better off taking a screenshot and putting that into Google Translate.
That way all the text remains in-place, and you can keep it as a visual reference to refer to.
If you were selecting text, it would wind up in a kind of jumble that would be much harder to use.