I think the word inventory is a great idea! I love that. Because you can design puzzles around which words the player will have access to at any given time, at it would be relatively simple to hold progression for the player until their vocabulary builds. I also don't think you would lose a sense of exploration and immersion. I would look to "The Witness" as a prime example of what looks to me like the game you are trying to build. The Witness is a puzzle game that reuses concepts and builds on them, and it is VERY immersive!
As for the Owl comment. Owl's don't mean anything in particular to Americans. Owls are owls. A horse, though, a horse means a lot to American culture. It is a cultural icon of transport, the old west, etc. We Americans cannot really see a horse and not think about cultural heritage. The same goes for Pandas in China, or Lions in Africa. So when I was looking around for owls in Insularum Raider, I wondered if Owls were chosen because they represent something to Latin speakers, or, primarily, the culture from which Latin originates! Does that makes sense?