Decrypting the Vanguard

The following is an excerpt from a scroll titled "Notes on Recovered Documents regarding the Vanguard", by Gasp, Air Genasi junior scholar in Zot Goran.
"Encryption Practices of the Vanguard
Members of the cult did not typically encode or otherwise hide their communiques, largely trusting to the notes not being read and for them lacking any context to explain what they were referring to. More permanent documents - records and information - were kept by only a few key members (see the section above on "Diamantina Everrage's Library") and these were indeed encoded quite severely. As I have worked with colleagues on decrypting them, we have come to call this code: the Angels and Demons cypher.
Not trusting to use devillish Infernal language, they used a code based in 2 other languages - Celestial and Abyssal, with characters altering irregularly from one to the other. Given that both use more complex characters than Common's sound-representing letters, it would take someone absolutely fluent in both to translate them - hence we have had to pool our resources to ensure we had a team with the knowledge to be able to decode this in the first place. There is also a pattern in their usage, where the Celestial characters appear to be literal while the Abyssal characters are more oblique.
Hence, learning the secret histories of the Vanguard will be a project of years, which I suspect will prove a relief to some who do not wish to dive headlong into the terrifying history of K'ul Goran we are beginning to understand and will prove unbearable to others who do not want this crucial information fed to them in crumbs. Even at the time of this writing, we have only just completed translating the titles of each document or book retrieved from Senator Everrage's study, and others. To be able to triangulate our sources and not rely on any single document for accepting things as fact, we have quite the task ahead."