How fantastical is the setting? You could have just "fairy chests" or whatever that reward those willing to find them, and solve their puzzles. I don't also see why you couldn't just copy the moredhel idea, you know, enemy troops using them for communication and equipment and such. It would also be cool if you had to work to even be able to read them, not just automatically having a party member understanding them but having to actually find a person or a spell somewhere that makes them readable. Could be a cool quest, you find a chest with unintelligible text that you cant open, so you must ask around doing a bit of detective work to find a person/spell to help understand it. The chest languages could be different too so you have to learn ways to decipher multiple languages or runes.
Like, the fairy chests could be your common riddles like those in BaK, maybe the enemy chest would have an answer that makes it easy for the enemy, only something their kind would easily know, like "who was sacrificed at Betrayer's River that earned it its call name?", and you have no idea what river that even is, so you'd have to learn the games lore and locations and stuff to find the answer. It would be nice to also be able to mark the map with the location of the chest for later return and also copy the chest text to journal with a button once deciphered so you don't have to return to the location later to look at the puzzle. Depending on the chest's theme the loot would be a bit different. And why so many word chests? Maybe some ancient race (faeries) the the idea first and others just copied it later.
Just some fun ideas I had, lol.