Could someone tell me how to say in Korean:
1. mustn't [it is forbidden] {One mustn't kill people.}
2. don't have to [it isn't forbidden but unnecessary] {I don't have to clean my room.}
Those are some ways to say unnecessary or forbidden things in korean
~은/는 금지되어 있습니다(It's forbidden to~)
~을/를 금합니다 (We prohibit to~)
~하면 안됩니다(You shoudln't do ~)
~하지 마십시오 (Do not ~)
~하지 않아도 됩니다(It's ok if you don't~)
~할 필요는 없습니다(It's unnecessary to~)