Maybe some examples would clear things up.
You're sitting in the garden, a neighbour walks by and says: "Hei, hvor er faren din?" (Hey, where is your father?) and you answer: "Han sitter inne!" (He is sitting inside)
Your neighbour will most likely not react at all to your phrasing, and just understand that your father is literally sitting inside the house. There is, however, a tiny little chance he'll make prison a joke if he is a real clown. If you want to avoid this, you can add what he is doing, for example: "Han sitter inne og leser" (He is sitting inside reading) This would never, ever mean that someone is in jail reading.
However, if someone you're dating suddenly asks you "hvorfor besøker du egentlig aldri faren din?" (how come you never visit your father?) and you answer "han sitter inne" - there is no doubt you mean he is in prison.
The direct translation of an equivalent in Finnish would be: 'He is sitting' (Hän on istumassa) using one of our more exotic cases: the 'inessiivi', answering the question "where". You can have fun with the different inflections here: https://www11.edu.fi/ymmarra/index.php?moduli=verbit&sana=istua
The other often used equivalent of serving time would be directly translated: 'He is inside the stone' (Hän on kiven sisässä).
Although it is used for both, I'm assuming here it is being used as a general statement of where the man is. If I were to use this statement in Norway would everyone automatically think I was talking about jail, or is it common to use it to relay location. I want to be culturally accurate.
Nobody would think you were talking about someone serving time. It is quite clear by context what you are meaning when you say this. If it was possible that the person you were talking of actually could be inside (a house), and you meant that that person was serving time, then you would want to rephrase your sentence. e.g "Han sitter i fengsel" or something like that.
I've searched the comments for more context, and I can see how this would make sense for "he sits inside" but "he is serving time" doesn't make sense. From an American cultural perspective, that means this person is in prison or jail, but as a translation, I just don't get how that translates and works in context. Any explanation? I think if I were to say "Han sitter inne", I may never mean it in the sense of "he is serving time", but more in the literal sense.
As you pointed out, there is a dfifference between the American cultural perspective and the Norwegian one.
I think if I were to say "Han sitter inne", I may never mean it in the sense of "he is serving time", but more in the literal sense.
If you said this in Norwegian to a Norwegian person, they might understand it as him being in prison, so it is important to learn that translation here, don't you think?
So what I'm asking is, what does this statement mean culturally in Norwegian? No, I do not know that a Norwegian might think the man is serving a jail sentence if I say "He is sitting inside" in its literal sense. I just imagine that would mean I'm referring to a dude sitting in a building, but that is what I'm trying to understand. What is the cultural context of this translation, and how do I use it properly? I'm just trying to figure it out. I kinda don't need any condescending remarks.