Hello,
I have the same problem as Koen.
I think he means that you can’t translate the product description that is in the product meta box (there is also a product description box (so that the description is located near the add to cart button).
When we put the product description in the normal text editor in wordpress then we can translate the description with wpml.
So I think it is best that you build in a solution that you can choose where the content of the description is (in the original wordpress area or in the product meta box).
Duplicate a product is not a solution because you can’t directly edit the translated. However you can change that in the settings that you can edit the product translation in wordpress itself but when you click update I won’t actually update the translation.