Hi @Matz Höög ,
I installed the same Swiden Language Pack and the latest CU Update like this:
Also works in sub site permssion set page when resolve user in People Picker:
In the first capture in the original question, I see the ribbon is not loading compeletly, I suggest you could try to clean browser cache and try again to see if it works.
Also try in other site collection to see if the issue still exists.
If still the same issue, I suggest to check the ULS log for details.
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