In defense of T'Pau and her unusual grammar:
So in "Amok Time," (right before Spock goes into heat) we meet T'Pau, this grand high elder of Vulcan who is officiating Spock's wedding/fight to the death.
She has a very specific way of talking. Some examples:
"Thee names these outworlders friends. How does thee pledge their behavior?"
"If thee wishes to depart, thee may leave now."
"Are thee Vulcan or are thee human?
"I grieve with thee."
If this is supposed to sound archaic and Shakespearean... then it's just completely wrong. "Thee" is not even slightly conjugated. If you're using thee/thou/thy correctly, that first sentence should be:
"Thou name'st these outworlders friends. How dost thou pledge?"
BUT my point is, I don't think this is supposed to read as "archaic" (also, if that were the case, wouldn't the universal translator just kinda auto-update the vocab?)
What is actually going on is Quaker Plain Speech.
Thee/Thou/Thy used to be English's set of informal pronouns, which you used for close friends and social inferiors. The Quakers came over to America in the 1600s, and were very into the idea of simplicity and equality for religious reasons. No titles, "Friend" as the default address, etc. They also artificially got rid of You/Your/Yours, English's *formal* pronouns, because they were what you used for talking to a social superior, and they were trying to get away from that sort of thing.
Skip forward like a hundred years. Language changes. Standard English drops Thee/Thou/Thy completely. The Quakers KEEP the pronouns, but the usage simplifies. Now they basically just have "Thee," and use it for everything, and don't conjugate the verbs around it in any special way. "In the eighteenth century, "thou hast" disappeared, along with the associated second-person verb forms, and the otherwise strange "thee is" became normal "plain speech."
Which is EXACTLY how T'Pau talks.
(I found this scene from The Philadelphia Story (1940) where Jimmy Stewart walks into a Quaker library, and the joke is that the librarian talks to him in Plain Speech - "What is thee wish?" and he (confused) responds in Shakespearean English - "Dost thou have a washroom?")
So I think that when Theodore Sturgeon wrote "Amok Time" in 1967, T'Pau's style of speaking was meant to communicate not necessarily "old-fashioned" but more "religious/ceremonial" and maybe "isolated." Especially since he's from New England, the right spot to run into Plain Speech in the wild.
In-universe, I think that (because it's a very important occasion) T'Pau is speaking a hyper-simplified, hyper-logical ceremonial Vulcan dialect, which the universal translator is rendering as the most stripped-down and "plain" English style of speaking possible.
