1. The current listing of documentaries lists them all, from A to Å (Kategorier => Dokumentar), old and new alike.
   The following URL have categories like "Nye dokumentarer", "Klimakrisen", "Sanne krimgåter" etc, which is much better in my opinion:
   https://psapi.nrk.no/tv/pages/dokumentar
   
   
2. Some content have more than one available subtitle, like "Matsjokket" episode 1. For some reason I get the english one for this episode. I have not tried other episodes.
   The plugin should handle cases where there are several subtitles to choose from, either through own settings or by checking Kodi's settings about preffered language.
   

python:
session.headers['Referer'] = 'https://tv.nrk.no'

session.headers['Accept'] = "application/vnd.nrk.psapi+json; version=9; ludo-client=true; psapi=snapshot"

• "nor" is norwegian subtitle where only foreign language is texted.
  
• "ttv" is norwegian subtitle where all language is texted.