两者均可译为“多久”,但有区别:
1.how soon 指再过多久,主要用来对表示将来的一段时间(如:in an hour,in two weeks 等)提问.如:
A:How soon will he be back?他要多久才回来?
B:In an hour.1 小时以后.
2.how often 指每隔多久,主要用来对频度副词或状语(如:once a week,three times a month 等)提问.如:
A:How often does he come here?他(每隔)多久来一次?
B:Once a month.每月一次.