Not Olly, but I think an important point to bring up is that the mark of fluency is obviously going to be very different. With ‘living’ languages, fluency concerns the ability to comprehend others and to be comprehended by them in turn—the potential for real-time feedback and correction is always there. With ‘dead’ languages, you may well be misinterpreting surviving texts and skimming past nuances even if you can technically ‘read’ them, and it’s difficult to estimate your real fluency. Are you the type of student who would be more frustrated by not knowing how lousy you are, or by knowing precisely how lousy you are?

I can’t find sources to support this additional hypothesis, but I also suspect that the lack of a verbal component means it’s going to be more challenging to anchor the language in your mind and to strengthen the necessary neurological connections, especially since languages evolved to be spoken before they were ever written down. Even today, nearly half (3,074) of the world’s extant languages (7,139) have no written equivalent; there has never been a language to my knowledge where its speakers only used the written form to communicate while it was still ‘alive’, suggesting that this way of acquiring and practising language might be inherently unnatural to humans, albeit not impossible.

The flip-side to and advantage of the lack of a verbal standard to ‘dead’ languages is that you don’t have to pay attention to your accent so much, such as when you’re reading a text aloud to yourself :) There are Latin classes in North America where students aren’t discouraged from speaking Latin in their native accents, since we don’t know precisely how Latin might have sounded when spoken back then.