Henceforth means from this moment forward: starting now, and then for all the time after. You meet it in law, notices, and rather grand speech: Henceforth, this building will be closed on Mondays. In ordinary talk almost everyone says from now on, and that sounds more natural. Though actually, even in writing, henceforth can feel a little stiff, as if someone is laying down a rule. It is only about time, not about reason. The shorter word hence can mean for this reason, but henceforth never means therefore. It is an adverb. You do not use it about the past.

從此以後、今後（偏書面、規定口吻；口語多說 from now on）