In addition to the previous error I also noticed that I wasn't able to translate/find the string "Group Name" for the plugin Learndash Group Registration (wdm_ld_group), the string is on the checkout page (hidden link). In order to see the checkout you need to add one item in cart on the product page (hidden link), select "Mehrere Konten" and add a company name into the "Firmenname" field. The string is also referenced then in the confirmation email to customer after buying.
I have checked your other issue, and have tried my best to make it work, but seems it would need a bit further work.
Note this addon plugin is not on our official Compatible plugins list so some issues may happen, We try our best but sometimes author collaboration is needed.
Please also invite them to our GoGlobal program in order to make the addon WPML compatible and our team would be glad to help. We will also try to contact them from our side.