[Gelöst] Attributes not showing up in translated product feed

Background of the issue:
I am trying to import a translated product feed on magnetarheat.com, but the attributes are not showing on the webshop. I noticed that attributes cannot be translated in the products editor, and WPML has another page for translating attributes. However, many attributes from the Dutch webshop are not visible there, preventing translation. I also couldn't translate this in the 'string translations'. Link to a page where the issue can be seen: versteckter Link

Symptoms:
The attributes are not showing up in the translated product feed. In the backend, attributes cannot be translated in the products editor, and many attributes are not visible on the WPML translation page. I expected to see translated attributes under the 'Specifications' tab, but instead, I got non-translated attributes.

Questions:
Why are the attributes not showing up in the translated product feed?
How can I translate the attributes that are not visible on the WPML translation page?