[orbital-decay]

Claude can speak medieval and ancient languages but mixes up different time periods pretty often, unless you hard prompt the desired grammar. For Old English in particular, it tends to give something vaguely Shakespearean instead. It often uses period-incorrect alphabet or modern characters as well (for Slavic languages in particular).

I've also tried Old Norse, Ancient Greek, and Old East Slavic, and the result is pretty much the same. For OES in particular, it often outputs period-incorrect grammar, writes in Old Church Slavonic (different language), or even modern Russian or Serbian. Looks like the dataset was a bit chaotic, with religious books mixed with old manuscripts and even modern books for children. Mentioning a specific work from the desired period makes it write better, and wrangling it by specifying the rules makes it get this almost right.