Dear Ernest, I have found something and trying. I have temporary remove your custom function
so sorry my english very bad.
When I changed english language products permalink. wp or wpml (I don’t know) redirect turkish url to en url and working. (all product duplicated with wpml duplicate function and wpml duplicated all products title and permalinks to english language)
please go to this url, wp redirect url to english url
https://maksdisplays.com/en/urun/pop-up-stand-corner/ => https://maksdisplays.com/en/product/pop-up-stand-corner/
please check it for me about this issue is true or false