I wrote " They need more staff" that was wrong...the answer was " They need much staff" which sounds weird
"They need a lot of staff" does also work. It's wrong to say that they need more staff because that would be "mer", not "mycket", in Swedish. The sentence tells us that they need a lot of staff, but it doesn't tell us weather they have all staff they need or if they need more to get as much staff as they need.
The way to say it in English would be "they need a lot of staff". Using much in this context just sounds weird
Although I consider myself a native English speaker, my grammar leaves much to be desired.. Would "they need many staff" work too?
No, that wouldn't sound right. 'A lot of staff' or 'lots of staff' sounds more natural