From what I understand, the spell-checker in the Windows version is Hunspell, and the spell-checker in the Mac is something else (don’t remember offhand).
They use different dictionaries. The dictionaries are not created by L&L; they merely selected them.
Other dictionaries can be added to Scrivener (second post in this thread: [url][JH] Dictionaries - Portuguese - #7 by ricardofdiogo]). A number of sources for hunspell dictionaries are available, and one post (in this thread: [url][NB] On dictionaries... - #3 by rwfranz]) lists several sources.
I don’t know Norwegian, so can’t really offer any comments on the quality of any of those dictionaries. If you find another source for hunspell dictionaries (even if limited to just one language), please reply to that list of sources and mention its URL.