It's a common Indo-European trait. :)
- Spanish: amigo - enemigo
- English: friend - fiend
- German: Freund - Feind
Swedish "vän" and "fiende" aren't really alike, but we do have "ovän" as well.
"It" is often used in English for indeterminate people. When the doorbell rings, we ask "Who is it?" and they reply "It's me." In the meantime, your roommate says "Don't open the door, it's an enemy!" Det would be used in each of these sentences in Swedish.
I think what you're saying is that 'it' doesn't make sense because we're talking about people. But an enemy can be a person or a group. If we're talking about the former, to use 'it' would not make sense. But if we we're talking about the latter, it might. Let's say two kingdoms—we'll call them Rhizaria and Alveolata—are warring. If someone in the court of the Rhizarian king mentioned the Kingdom of Alveolata, the King of Rhizaria might say of that kingdom, "It is an enemy."
Grammatically speaking, I think this is like what you'd say if you were knocking at a friend's door: "it's me!"
It should really be 'There is an enemy in English'. "There is/are..." for things that exist. But because "Det..." can be both 'it' and 'there' in Swedish, Swedes often incorrectly use "it" for people.
No, we'd say e.g. det finns en fiende for that in Swedish. The phrase det är en fiende would never mean "there is an enemy".
“It’s my husband” ... Swedish is not incorrect, no language is. But let English be held to the same standard.
Please stick to feasible translations instead of technically correct but very unlikely ones.