i dont have much faith in this movie,
the whole camp is supposed to be a different nationality and language than americans.. so it already kind of screws with the established facts of the original movie.
I've got a feeling that a majority of the Norwegians at the camp knew how to speak English, but the last two that ended up surviving the aftermath to chase the Dog-Thing to Outpost #31 probably had one who did and one who didn't. And its likely the one who could speak English was the one who handled the grenade and got blown up, while the one who didn't know how to speak English was the one that Garry shoots.
Another possibility is that they both could speak English, but due to the emotional stress of the events they've gone through, the one who shot at the Dog-Thing and eventually got shot by Garry, was probably so emotionally stressed to think straight and that he needed to speak English. From what I've seen in other films, with characters that speak two languages, they normally revert to their native tongue when they're frightened or angry (which makes sense form a psychological point of view, because if you knew two languages, would you swear in English if you were frightened out of your wits or would you swear in the second language you had to learn). A good example is Monica Bellucci in
Irreversible. Before she is raped, she tries to get away from Le Tenia after witnessing him beating the prostitute. At one point, she screams "help" in Italian. Since the film itself had no script and dialogue was improvised by the actors and actresses, it's safe to say that at the moment (at the choice of the actress), Monica's character would have been so frightened, she'd scream in her native tongue.
So, it's possible that there may be characters in the film that speak fluent Norwegian and English, while there are those that do not know how to speak English and need translators. From what we know of the first film, there was never any indication that there wasn't anyone who didn't speak any English at the Norwegian camp. With the information we have, we know a majority of the people at the Norwegian camp were Norwegian. So, the possibility of one, or at least two, being American is still possible just by what is presented in the first film alone, as we don't have a lot of info about the Norwegian camp and the individuals there from Carpenter's film. All we got from Carpenter's film about the Norwegians is what they were doing, where they found the ship and a foreshadow of what was going to happen at Outpost 31. We do not know anything about who they were, if they could speak English as a second language or how all of them came to their demise (only about three individuals do we know for sure, the rest we assume became things or were killed because they were thought to be things).