What is the punishment for reviling or insulting in Islamic Sharia, especially in a country not governed by the law of Allah, and how can the offender be deterred without injustice?

The punishment for reviling and cursing is discretionary (ta'zeer), and it falls under the authority of the Imam or his deputy. Individuals are not permitted to take revenge on those who revile them by beating them or breaking their bones, unless the Imam specifies the discretionary punishment with a known duration and a known location; in that case, the aggrieved party may carry it out themselves. As for returning a reviler's insult, it is permissible, provided it does not involve aggression.