Posted this on Reddit, no one there noticed it so I thought I'd post here too.
So in "The Lich" they go around Ooo taking gems out of all the "crowns of power". The Ice King's crown was an obvious - it gives him magic of course, makes sense it'd be a "crown of power". But what about all the other princesses? They never are shown using magic because of the crown.
And then here comes another question: If the gems in the Ice King's crown are magic themselves, and part of the Enchiridon's magical key to opening portals... how? The gems obviously existed before the Mushroom War, as the Enchiridon did (as we learn in I Remember You with Simon Petrikov, the future Ice King, having it in the newspaper clipping) and it seems the Ice King's gems were fit into it.
Which means that the Enchiridon was made during the same time as the Ice King's crown's gems, and all the gems were made at the same time to function as a key.
So it predates the Ice King's crown or is from roughly the same time, obviously.
We could assume the crown itself predates modern civilization, it was found in Scandinavia. So most likely Viking or related to Norse Gods. That means the crown most likely was made during the time of the Vikings, possibly before them in Pre-Roman Iron Age Scandinavia. That puts it in the BCEs. Meaning that by 2000 (we should assume that Simon found it in the 21st century or late 20th century) it was already almost 3,000 years old - a vestige of ancient, forgotten magic.
The Enchiridon must have been there with it. As we know, Enchiridon is Latin for "handbook" and Greek for "manual". While Simon found it in the Hindu Kush according to the newspaper clippings, it was seemingly made by some Greek and Latin-inspired individuals.
In another thread, http://i.imgur.com/89ofj.jpg was linked. This resembles in my opinion some sort of runes. Some look a bit Asian-inspired though.
The Ice King's crown was found in Scandinavia, the Enchiridon was made roughly the same time (the gemstone in it seeming to be a key somewhat confirms that) with a Latin or Greek title. This would suggest it having been initially written in Latium or Greece. Most likely Greece as it is the most writing-related part of the ancient world.
Yet some of the text in it resembles runes. Runes, as you may know, are associated with Scandinavia frequently. Ignoring the seemingly Asian-inspired characters, here is a list of runes from Scandinavia:http://2.bp.blogspot.com/_oRfR-qKcJP4/TG2DCKs2ulI/AAAAAAAAEEw/_B60KThAlOA/s1600/runes.jpg
Immediately, similarities are seen. A backwards Lagu at the start of line one and an Inguz at the end. The second line has what looks like the Japanese nn to me, but I can't be for sure.
So it's obviously not a real runic alphabet, yet it has remarkable similarities to the runic system.
So parts of it are in English, we can assume that's for our benefit mainly. Translations are usually in copies. The Enchiridon is obviously not a copy.
What seems more likely is that whatever society had the Ice King's crown initially was part of a larger ancient civilization that had knowledge of the multiverse and travel throughout it, knew how to make it so that the Enchiridon would harness the powers of the gems, could create the gems, and so forth.
tl;dr: The Enchiridon is well over 4,000 years old and so is the Ice King's crown. They were made by either one civilization or a union of civilizations in Pre-Roman times (Hyboria? haha that'd be an amazing reference, and it'd also give us Cthulu!) and this civilization was highly advanced in magic (if not technology as well). It fell for some reason, Simon uncovered two artifacts from it (the Ice King's crown and the Enchiridon), possibly more.