The Oracle is a great idea. Of course, the real Oracle never gave a straight answer, though.
So... maybe instead of the notoriously capricious Oracle it would be better for players to visit the Library of Alexandria with it's rich repository of the ancient worlds' knowledge, I'm sure the Chief Librarian would give dependable answers.
Darn it, I really should type slower and pause before I click "Post".
After thinking about this more, something even better than the Library at Alexandria would be a building that becomes available in every home city when that specific culture reaches level 40. This way players don't have to "travel" to Alexandria to find the information (which would involve the loading screen as they transition to a new location).
The information that is available at the building would be the same for every culture, that way there is only a single background script that is used at all locations rather than custom scripts for each culture, but the building itself would be based on the architecture of each culture.
If you want to take the easiest route it could be as simple as a temple dedicated to the god/ess of knowledge/wisdom for that culture, of if you don't want to keep re-using god/esses that are already being used elsewhere in the game it could be a place of learning and knowledge that is dedicated to someone appropriate for each culture (I'm betting that you already have a building that could be used for this in each culture). Personally I prefer this latter route, especially when there is someone associated with the alphabet/writing of each culture.
* God/esses of knowledge/wisdom (shamlessly copied from wikipedia)
, if you want to use a temple as the building
Celtic - Ogma
Greek - Athena, Cecrops, Coeus, Metis
Egyptian - Neith, Isis, Thoth, Sia, Seshat
Persian - Anahita, Ahura Mazda, Chista
Norse - Odin, Frigg, Saga, Snotra, Vor
Babylonian/Sumerian - Enki, Nabu, Nibada
Roman - Egeria, Fabulinius, Minerva, Providentia
* Divine/semi-divine creators of Writing/Alphabet/Speech, if you want to use a house of learning & knowledge as the building
In each case they could be called the "Library of <character>" or the "House of <character>", like the "Library of Cecrops" of the "House of Cecrops".
Some of these characters are also associated with making predictions, for example Carmenta was also a (minor) goddess of prophecy, and Enheduanna was the high priestess of the most important temple in Sumer, which fits in with the idea that legendary gear is not guaranteed to drop, you're undertaking a quest based on the wisdom stored at the house of learning and you hope to be rewarded upon success.
Celtic - Ogma
Credited with inventing the Ogham alphabet. He's divine, but that doesn't mean it has to be a temple in the standard sense, it could still be house of learning in his honor.
Greek - Cecrops
Legendary Athenian king who invented the Greek alphabet.
Egyptian - Seshat
Scribe of the gods, credited with the invention of writing and the alphabet.
Persian - Darius I
He claimed credit for the invention of Old Persian Cuneiform in an inscription on a cliff at Behistun in south-west Iran.
Norse - Mimisbrunnr
In Norse mythology Odin didn't invent the runic system, but he discovered is by making sacrificing himself. But since he's already head of the Norse pantheon I'm thinking that the Norse "library" would be dedicated to a lesser source of knowledge/wisdom. It could be as generic as the "Library of the Runemasters", or a little more obscure like visiting the "Mímisbrunnr", the Well of Mimir, who was a counselor of the gods, or maybe even the House/Temple of the Norns, the Norse version of the fates). Personally I like the Mímisbrunnr best, but your mileage may vary.
Babylonian - Enheduanna.
Techically she was Akkadian, the world’s first author known by name and was (possibly) the daughter of Sargon of Akkad (Sargon the Great). Whether Enheduanna was, in fact, a blood relative of Sargon’s or the title was figurative is not known. She is also credited with creating the paradigms of poetry, psalms, and prayers used throughout the ancient world which led to the development of the genres recognized in the present day.
Roman - Carmenta
According to the legendary origin given by Hyginus it was Carmenta, a Cimmerian Sibyl, who altered fifteen letters of the Greek alphabet to become the Latin alphabet and which her son Evander introduced into Latium.