The moment FNV's Caesar fully clicked for me was when I heard him pronounce "et cetera" as "et ketera".
Think about it for a second. This is a post-apocalyptic future where most knowledge of ancient civilizations has faded into obscurity. It's not gone, thanks to the efforts of the Followers and other factions, but even if you're a Follower you have to really go and look for it.
Now, our boy Edward here didn't just learn the broad strokes of Roman history - he's familiar with niche and intricate aspects of its political and military structure as well as its cultural practices. He knows the original meaning of "decimation". He knows the difference between a legate and a centurion. He knows the general appearance of a Roman legionary. And he knows Classical Latin, in its Classical pronunciation. Think how deep into the weeds you would have to look to find out that "Caesar" was actually pronounced "kye-sar" and not "seezer" like any English speaker would instinctively say it. And then how invested you would have to be that your whole army adopt this incredibly archaic pronunciation.
But the "et ketera" bit really takes this to the next level. "Et cetera" has been a common set phrase in the English language for centuries. It's not a fancy word from a long-dead language that Caesar exhumed from the depths of the Followers' archives. It's a regular part of casual speech that Caesar bothered to learn the etymology of and decided to retroactively apply the original pronunciation to. For no reason other than commitment to the bit.
This is not the approach of a scholar interested in learning the deep lessons of history. This is the borderline unhealthy obsession of a fanboy. He's the caricature of the teenage boy whose gateway into fascism is thinking a bit too much about the Roman Empire. An archetype that barely existed when FNV came out but has gotten awfully common since then. This game was really ahead of its time.
(Also in further support to this read, it's quite telling which things Edward Sallow did NOT bother to learn about Rome. Like very salient and well-researched points of historical analysis that help explain its rise and decline. For example the fact that Rome did not in fact typically stamp out local cultures, but actually often borrowed from them, allowing people to generally live in peace as long as they paid their taxes. Or their heavy emphasis on infrastructure building which meant people could see their lives materially improve as a result of Roman presence. Or conversely, how concentrating power in one man drawing his legitimacy from the military led to recurring civil wars which critically weakened the empire. All factors that directly run counter to Caesar's governing philosophy. Because his understanding of Rome is fundamentally aesthetic rather than political or historical.)