How is Zakat on wealth calculated, and how are the beginning of the Hawl (Zakat year) with a monthly salary increase determined, and in which currency is it calculated, and when is it to be given?

Zakat is obligatory on salary if the saved portion of it reaches the nisab (which is equivalent to 85 grams of gold or 595 grams of silver) and a hawl (lunar year) passes on it. 2.5% (a quarter of a tenth) is to be paid from it. The nisab is calculated based on the price of gold or silver in the local currency, and the month for paying zakat is the month in which a hawl has passed on the nisab.