International trade at Myra is based on a global gold standard. Most realms and countries in Myra are using this global gold standard also to fix the exchange rate to their local currency.
The standard economic unit of account is a fixed weight of gold, the GS (this abbreviation is mostly interpreted as "Goldstück", but it could be an abbreviation of "Gold Standard", too). If transferred to Earth, it would be equivalent to about two pounds of gold.
In some regions of Myra they use instead the term "talent of gold". Generally this refers then to the same amount of gold, talent (sometimes also talanto) being a measure of weight in this regions (but not as heavy as the talent of the bible which would amount to about 30 kg).
The german article Währung contains more detailed information regarding the currencies and the smaller coins used in some realms.