How to know which luxuries I'm trading for?

[player1 fanatic]

Simple question. If I buy some luxuries from the diplomacy, how can I know later, which ones I have already purchased and which I have not?

 

[Browd]

Unfortunately, there is no deal history display or resource origin display (the View Reports/Resources screen only tells you about resources in your cities, but not CS resources or resources in or out from trade). Hopefully we will get that in a patch.

 

[Iron Angel]

For now you will have to settle with writing down which luxuries you are trading and at which turn that trade deal runs out.
This is something that of course should be in the game. Information is a powerful weapon.