Hmm, good point. My guess is that the perspective is so tightly tied to John that there's no room to introduce a scene where we don't know whether or not he's real. It worked well to duplicate Sarah instead because we're still closely following John through his confusion (plus, she's the one with the twin).

That's how Russians bootleg for some reason. Instead of subtitles, they'll just dub straight over the original audio track so that you have both languages going at once.

It's super common in downloads I've seen. I have no idea why.