What is common knowledge in Varisia regarding Thassilon, the Runelords and their domains?

[Kiniticyst]

Since the events of Rise of The Runelords and Shattered Star have pretty significant effects on the region, what is now known by common peoples about Thassilon?

I'm about to start running Return and am wondering what to keep mysterious and what people would widely know. Are the names of the 7 runelords common knowledge? Do people know that there were 7 of them? What about Xin? Do they know which regions of modern day Varisia were once Xin-Shalast and Xin-Bakrakhan? Do they know that the Irespan was a bridge that connected the two?

I had previously ran Rise with some of these players and one of them was an Oratory Bard that did his best to spread the tales of what the Sihedron Heroes did.

If these things are not common knowledge by everyday folk, What kind of knowledge history DC's should I be looking for for such things?
Would any run-of-the-mill scholar know about all of that? I'm aware that the Sihedron Council's scholars certainly know this stuff, is it reasonable that they have books available on it and that a 1st level character could have read them? Is the Thassilonian language more readily available to learn since the beginning of Rise?

Apologies that there are a lot of little questions, any advice would be great!

[Misroi]

I'd think it depends on how historically educated the person you're talking to is. If they're a turnip farmer who built his home in the shadow of some forgotten Thassilonian monument and tills his fields, then probably not - it's not really important to him. He probably knows that it belongs to an empire that died out thousands of years ago, but the questions of "who built it?", "what enemies did they have?", and the like don't put food on the table. Now, the Pathfinder Lodge in Magnimar - especially post-Rise? Oh yeah, they certainly know most of the details - the last Runelords of each nation, the basic history of Xin, that the Irespan connected to something that doesn't exist any longer, etc.

Based on how your table of Rise went, I'd say the populace is better informed than canon Golarion on how close Varisia (and by extension, the rest of the world) came to being controlled by a megalomaniacal dictator from 10,000 years in the past, so there may be higher interest in this empire, since they're not as long dead as everyone expected. As for your questions of "would the scholars have published books," or "is Thassilonian more readily available" - I'd lean towards yes, but it's your campaign.

[Phntm888]

I think Misroi hit the nose on the head. If you're looking for more hard line mechanical advice...

I'd say that the baseline Knowledge (history) DCs for the most basic stuff should be somewhere between 10 and 15 - e.g. knowing there were seven runelords, their names, and that they built some of the megalithic monuments scattered around Varisia like the Irespan and the Cyphergate. Everyone would know about how the Isle of Xin rose from the depths as part of the climax of Shattered Star and destroyed part of Magnimar, as an event like that gets talked about. Knowing the names of their individual domains would be a bit more challenging, and the locations of Xin-Shalast and Xin-Bakrakhan should be a bit harder than that since the are fairly isolated. Now, if one of your PCs from Rise has opened up Xin-Shalast to excavation or anything like that and widely circulated the means of locating it, that should lower the DC more. Similarly, if the Oratory Bard has been telling everyone about the awesome things they did for the past however many years, then the DCs would naturally be lower.

For the availability of the Thassilonian language, I wouldn't put any barriers to a PC choosing it as a language with either their point of Intelligence bonus or a rank in Linguistics. It's still something that someone needs to take the time to study, being a dead language and all, but there should be more teachers available than there were before Rise. Think of it as Latin in the real world - most universities and even some high schools teach it, but if you don't study it you don't know it.

Scholars of history and magic should probably have a decent idea of the basics, and the Pathfinder Society should have chronicles available, as well. Especially since every adventure in Shattered Star keeps mentioning at the end that if the PCs take a day to write up a summary of their adventure they gain Prestige and Fame within the Society.