I know you wrote this a while ago, but a teacher who "covers" for you is probably not a substitute or a temp, just another teacher covering your class for some reason. We don't use "supply teacher" in the US, but a "sub" is hired, usually from the outside, for a day, whereby other teachers might "cover" for another in a pinch.
In UK, we use term ‘supply teacher’ for a professional teacher who hired through an agency to cover an absent teacher(s) for a day or longer term (weeks, even months if needed). Cover supervisor – is a position at school for the person who usually do not have teaching qualifications whose role is to cover absence of teachers as well. Cover supervisors are cheaper and can be deployed with a short notice but cannot provide adequate education so both needed. But I do agree with you that 'cover' usually means that somebody within a school/company do the job in the place of absent person.
The church took it from Late Roman bureaucracy. The vicar of a diocese (meaning a secular province) technically substituted for the Emperor. Later the church appropriated the terms when it maintained its organisation during the collapse of the imperial administration in the western empire.
So I'm guessing (but could be wrong) that Norwegian has borrowed the word from Latin, in its original sense of 'standing in for someone else'.
It's the same Latin root, vicarius, from vicis, meaning change, alternation, stead: https://www.merriam-webster.com/dictionary/vicarious .
I'm sorry, I know this isn't related to the sentence, but, can someone help me? Yesterday, my activity stream was working fine. Today, it says "You're alone, PianoMaja, find some friends" i follow my 8 friends. Why can't I see the activity stream? How do I fix it? Thanks in advance!