what language register is sir tristram using in his conversation with king anguish on line 22 of the excerpt

He's using middle English language, and as we read the excerpt, we see that he is speaking more formal

The English language in general has gone through several variations; between what is known as the Old English language and Modern English, after the Norman conquest of England around 1100 and until 1500 Middle English was the form of English spoken in England; in Arthurian times with King Arthur Knights tradition, Arturian Literature and British mithology where Sir Tristan belongs to, the common language is Middle English.