So the French can trade for any resource correct, this works, what is buggy about it however is they don’t have to drop off the previous resource before you get a new resource.
For example if you need food and have a cart with 70 gold, you can hotswap the cart to food and it will drop off 70 food instead of dropping off gold and then having to make the trip to get food.
It specifically says it doesn’t work this way in the campaign or at least I think it did, anywho it shouldn’t work this way regardless. Also the trader still says it is carrying the previous resource, gold in the above example, leading me to think this is a bug.