I read somewhere that they are actually speaking both different languages, one of them Danish and one of them Swedish or something like that. Maybe for the security reasons?
I just got around to seeing episode 6 and my heart sank in last few minutes. I knew that this is how it had to end, but damn.. That was just sad. Rami Malek really pulled it off, it was very subtle performance, but it was exactly what I would expect from Eliot's character. Also the cinematography is so fucking weird I love it.