If the human race has persisted steadily enough over those 10000 years to have retained knoledge of our current languages, I doubt they would have let slide the knowledge of where the nuclear waste is buried.

I think the whole idea here is that a lot can happen in ten thousand years. Whoever is trying to go in there could be human or non human, could be advanced or primitive. Symbols are the best way to communicate in any of these events.