Comment 8 for bug 732139

For Widelands' style, I would prefer avoiding any type of direct currency exchange. Each player could instead increment/decrement a value for each type of ware like this:

- Yellow neutral symbol (default value, internally 0), meaning not-up-for-trading.
- Green positive value (internally > 0), meaning how much he needs (is willing to pay for) this type of ware.
- Red positive value (internally < 0), meaning how much he asks for selling this type of ware.

And then the system could automatically match the exchange of wares of multiple types in a single trading action whenever a carrier/trader is available for a transfer. Could also present the current lower values in the global economy, for the user to decide if he wants to match any of them.