While most nations have their own currency, there are certain commonalities to be considered.
Sovereign
In everyday parlance, a unit of a national currency is known as a Sovereign, usually preceded with the name of the minting country, and shorthanded as the number and the first three letters of the country in all capitals and a $. For instance, fifty Athaerian Sovereigns would be written out as 50 ATH$
Promise
The most international currency is known as the Promise. Its value is based on the amount of magical energy required to be exchanged to perform the simple cantrip of turning thin air into a precious metal, as determined by the Mages Guild. Countries that exchange their currencies for Promises are said to be on the Guild Standard. Usually the type of precious metal determines the unit. For instance a Gold Promise (GP) would represent the amount of magical energy needed to turn thin air into a standard of gold. While Promises can be stored as a coin made of the actual metal, it is more common to store the magical energy itself into an Elementai crystal.