The introduction to "Soldier of the Mist" says that archaic Latin is the written language of Lucius, and Greek is used is some places where others have written in the journal (ie Eurykles and Pindaros). However this brings up the subject of how Lucius reads these entries when he cannot read Greek, he barely speaks it, accordingly to himself. The way Wolfe has set up this whole language conception is interesting because in "Soldier of Arete" Lucius meets someone who comments that the Roman writes his letter A like " A ox's head." Which, in fact, was how the Egyptians and Semites wrote their A. But, Wolfe does say to us that Lucius uses Archaic Latin and not Latin as we know it now (Which developed around 114 AD). Oh, and Lucius' friend who took him home were Crimson Men, of whom Lucius was not of nationality, he just knew their language.
Xury
PS Why is Severian called the red-clawed master by Hethor? (One example is at The Claw of the Conciliator, ch 8, p288 of The Shadow & The Claw.)