"Min son går i sömnen varje natt."

Translation: My son walks in his sleep every night.

[Rebkova]

I do not understand, why is this not translating into "walks in the sleep" (due to sömnen). And therefore why "in his sleep". Wouldn't that translate into "i sin sömn"?

[Lundgren8]

Yes, but the set phrase ’walk in one’s sleep’ in Swedish is gå i sömnen (walk in the sleep). Swedish very often uses the definite form where English uses a possessive pronoun. See also this thread.

[alexgrossini]

so, "walk in the sleep" would be a correct meaning in swedish, but in english there is a set phrase for it and it would be wrong. I thought this was a course to learn swedish...

[Dayalura]

Using correct english in a english-to-swedish course sounds logical to me. What's your problem? I'm not native english and find it rather useful because it also corrects my english and I can learn both this way. Sure, it's a little more complicated but that's fine with me.