How often do you think Dipper would make a reference that no one gets and then instead of just explaining it, he actually shows them the original work? (translated, if they’re speaking a different language by that point in history)

He certainly tries, but even translated, some things don’t age well. Especially fantasy things.
(Also, Dipper has to end up translating the things himself, and a lot of the language ends up archaic or clunky because languages never translate directly all the time).