Currencies in Islamic law are only permitted to be exchanged at spot (today) according to AAOIFI Shariah Standards. Certain structures based on Murabaha or Waad do replicated the outcome of a forward currency exchange.
A conventional Forex swap is the exchange of two loans in different currencies of equal value at spot, which are both paid back at same date in the future. This implies a forward rate of the currencies involved. The loans at spot are netted and not paid out.
An Islamic Forex swap could be replicated by use of two Tawarruq in different currencies of equal value at spot:
A sells to B 1000 USD of Platin at 1050 payable after one year. B sells A 750 Euro of Aluminium at 780 Euro payable after one year. Exchange rate at spot is assumed at 1.33.
After one year 1050 USD have to be paid by B and A has to pay 780 Euro to B. This implied a currency forward rate.
See also: Islamic Derivatives.