u/Global-Chance-2717

I typically like going straight to the most comprehensive grammar possible when learning about a language, but I've noticed that many languages don't have an authoritative grammar book for them. For Sumerian you have Jagersma; for Japhug you have an absolutely massive 1500 page grammar book by Jacques, but for languages like ancient Chinese there seems to be quite few resources (in English at least). What are some of the most obscure languages you guys know that have been comprehensively studied?