I had this issue, how I fixed it was copy and paste Trader file 2-3 times. it fixed it for me
also make sure all your files are correct layout when editing, as I found out extra spaces etc can mess it up

I've copy and pasted the Trader file 8 times already, and it's still not working for me.

Same issue here. Trader is the only mod present, and still nothing. Does anyone have an example of a working one?

have you found a solution?

Missing Trader data error in chat is fixed by adding a mod called Trader Fixes and Features. No idea what you broke though. Didn't need to uninstall this to fix that error.

This mod is pretty simple. Install it like a normal mod then put the Trader folder, with the five txt files, into your profiles folder. This gives you the two default traders on Cherno. If they aren't showing up you did it wrong.