If you more or less follow this walkthrough, you'll achieve fluency in the Yucatec Ancient Dialect around the time you explore the ABANDONED VILLAGE the second time. This will enable you to read the Fluent Yucatec monolith (5/7) in the Temple District. The monolith is due east of the temple entrance, on the dais where the masked orator is preaching to a small but enthusiastic group of citizens.
Reading the monolith reveals a clue: "Seven golden birds perched here and there. One escaped to the trees with his treasure. Dropped from his talons, I'm waiting for you."
Selecting the monolith on the in-game map reveals the area in which the hidden treasure can be found.
The "golden birds" in question look like this one, attached to the archway near the monolith.
The one you're looking for is near the top of the stairs south of the monolith. At the top of those stairs...
...is the Proficient Yucatec monolith (1/7), which you probably deciphered earlier.
Turn around to face the stairs and you'll spot the golden bird hanging from a tree branch. One of the outcasts from the Dice with the Dead Side Mission is also standing here.
The monolith riches, survival cache (22/34), is buried in the corner behind the outcast.