Trying to think of something not overtly based upon mythology--Wendy Walker's The Secret Service?
Novels set in M. A. R. Barker's Tekumel (Empire of the Petal Throne) rely heavily upon the reader's familiarity with Barker's EPT materials, which include enough worldbuilding for several languages, the customs across thousands of years of several distinct cultures (at least two of them non-human), etc. They are not particularly great novels, but I think they might qualify, insofar as the ones I've skimmed have been written primarily for a readership presumed familiar with EPT, without much translating backfill/incluing.
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Novels set in M. A. R. Barker's Tekumel (Empire of the Petal Throne) rely heavily upon the reader's familiarity with Barker's EPT materials, which include enough worldbuilding for several languages, the customs across thousands of years of several distinct cultures (at least two of them non-human), etc. They are not particularly great novels, but I think they might qualify, insofar as the ones I've skimmed have been written primarily for a readership presumed familiar with EPT, without much translating backfill/incluing.