Being a native speaker of Norwegian, I can confirm that yes, the subtitles for many lines are wrong. In a few cases they are actually so bad that the meanings are totally different.
I've made two subtitle (.srt) files where I've replaced the worst ones with my own corrections.
Download corrected English subtitle file with only Danish and Norwegian lines.
Download corrected English subtitle file with Danish, Norwegian and English lines.
All of Sander's lines are in Danish. Norwegian and Danish are mostly mutually intelligible. I have also received help from the native Danish speaker Janus Bahs Jacquet in the comments and from two Danish friends of mine elsewhere.
Warning 1: The following answer (quite obviously) contains spoilers.
Warning 2: This answer contains crude and vulgar language and also parts of an extremely unpleasant, nasty joke by one of the Norwegian characters.
Note: The Norwegian characters speak in somewhat different spoken dialects (mostly West Coast Norwegian and Northern Norwegian), but I've transcribed everything in standard, written Norwegian (Bokmål).
I will explain the errors, and what they actually say. I will use the following formatting pattern:
00:00:00 (Occasional comment from me.)
What the subtitle says.
Transcript of what is actually said in Norwegian or Danish.
I have come across two different subtitles for this movie. One of them only includes subtitles for non-English lines. The other one has subtitles for the English ones as well. Where they differ, I have included both. The one that only translates non-English lines is always (I think) listed first. If you come across any other English subtitles for this movie, please let me know.
I'll start with the more serious ones:
00:02:16 (This line is much more correct in the other version.)
Where is it? I don't see anything.
Hva i helvete er det vi ser etter?
What the hell is it that we're looking for?
I'll let you know when we get there.
There is another, equally wrong, version of this line in the other version:
A little bit more or else we will be flagged on the site.
Vi begyner å nærme oss kilden til signalet.
We're closing in on the source of the signal.
You know women...
This line was not spoken at all. The subtitle author must have just made it up or seen it in the original script or something. It's in both versions of the subtitle.
Turn on the lights.
The other version has a take on this line that doesn't even make sense:
Sander (He's greeting Sander.)
00:44:35 (This line is in Danish.)
You made a mistake for bringing these people here. More people may
Hør nu hvad jeg siger til dig. Edvard, det er fuldstændig vanvittigt at bringe folk ind i det her udefra. Vi kommer til at miste det vi har fundet.
Listen to what I'm telling you. Edvard, it's absolutely insane to bring people into this from the outside. We'll lose what we have found.
(Sander is arguing that they should not call for outside help, as that may lose them their sensational discovery of an alien life form.)
00:44:41 (Response to the line directly above.)
Sander, we do not know even if they are dead.
Sander, vi er jo langt forbi det punktet nå.
But Sander, we have passed that point long ago now.
(He's telling Sander that given the dire situation, they should no longer be worrying about the discovery.)
Let's finish them off!
Kom igjen, din jævel!
Come on, you fucker!
De er vekk.
They are gone.
They killed him!
The other version has:
Lars is killed
De dreper oss også!
They're gonna kill us too!
Lars, it's me.
Vær så snill!
Please! (Literally: "Be so kind.")
Do what I say, now!
Vis meg tenna dine!
Show me your teeth!
It's me Matias. Lars, it's me, Matias.
Hva faen er det som har skjedd? Lars, hva faen er det som har skjedd?
What the fuck has happened? Lars, what the fuck has happened?
That's no dog. Start the helicopter, now!
Det er faen ikke mulig. Start det jævla helikopteret nå!
It's not fucking possible! Start that damn helicopter now!
Here are some relatively minor, inconsequential ones:
I remembered a joke.
Jeg har en bra en her nå.
I have a good one here now.
Hør den her.
Listen to this one.
A man and his wife were having sex one night...
The other version of the subtitle actually names the husband:
Seorg and his wife were having sex one night,
Gubben og kjærringa ligger og knuller ut av ville helvete.
A man and his wife are in bed, fucking wildly as hell.
He uses very vulgar language full of slang, including crude, nearly offensive terms for "husband" and "wife."
Okay. Continue the joke.
Ja, gutten og kjærringa, fortsett.
Yes, the boy and the woman, go on.
The boy is on top of his grandmother... Having sex with her!
Og der ser han faen meg lille Sven ligge oppå farmor. Og bare gir henne jernet!
And there, he goddamn sees little Sven on top of his paternal grandmother, just giving her the iron!
00:03:00 (This line is much more correct in the other version.)
You play with mine so I play with her, right?
Det er ikke så artig når det er din egen mor, er det vel?
It's not as fun when it's your own mother, now is it?
Let's go Lars, okay?
The other version has:
Lars, you're okay?
Lars, vi må komme oss inn.
Lars, we have to get ourselves indoors.
Nå viser du tenna dine!
Show your teeth right now!
She is smart.
Where is Lars?
Hvor i helvete er Lars?
Where the hell is Lars?
Lars? Lars, it's Matias.
Lars! Lars, for faen, det er meg, for faen!
Lars! Lars, for fuck's sake! It's me, for fuck's sake!
The lines not mentioned here, although often not translated very well, are mostly fairly alright.
But I think there were some things that were said in Norwegian and/or Danish that were simply not subtitled at all. I don't want to watch the whole movie again. But if someone gives me the timestamp of such a spoken line, I will edit it into this answer.