One of the key aspects of his character that shines through in all his dialogue is how earnest he is. He sees no point in pretending to be something he is not or being coy/circuitous in his speech.

While his speech can be blunt and rather short to those he is irritated with or who are of lesser status, Zenos’s language never becomes outright informal.

• Contractions are only used sparingly in his speech. Per my count, he only ever uses contractions in the following lines—5 times across his entire screentime in the game.
  • [SB] Zenos yae Galvus: You're better than most, I'll grant you that. But not good enough. This ends now.
  • [SB] Zenos yae Galvus: And that is very admirable. However, I've had enough of this dumb show. Give voice to that hunger I see in your eyes, or I will pluck them from your head.
  • [EW] I don't want your help. Zenos viator Galvus: And I'd rather not give it. Nay, I would have preferred that we enjoy a private reunion.
  • [EW] Zenos viator Galvus: Yes, yes! Rise once more! It mustn't end yet!
    • [Why hello final battle innuendo…]

He’s bored to an appalling extent by the tedium of existence. He literally looks upon his countrymen killing each other in a frenzy after the death of Varis and just says: “Boring, boring, boring…” He may be verbose, but the man’s dopamine reserves are about as dry as Death Valley in July.

• Especially in Endwalker, his dialogue remains melodramatic and hammy, but there is far less of the unhinged joy and fervor that was on display in his Ala Mhigo/Royal Menagerie scenes. You could call it a tantrum or depression that the Warrior of Light isn’t paying enough attention to him, but the general discontentment seeps into his mood throughout the expac.

A fun sampler of some of Zenos’s wordiest diction choices:

• heretofore (used both in SB and EW)
• ephemeral
• transcendent (he uses this one, as well as “transcend,” a lot)
• tepid
• noisome
• pretensions
• slavering
• vicissitudes
• succor
• conflagration
• incandescent
• ravenous
• banality

He uses “mayhap” frequently, as well as “perhaps” (and he is very unlikely to use the word “maybe”). There’s a fascinating script analysis chart created by the person behind xiv.quest that offers a basis for comparison of formality between different characters:

Source: https://eriyu.tumblr.com/post/771228712765194240/i-noticed-a-while-back-that-lyse-alisaie-and

It’s often easier with Zenos (or any character with unusual/formal speech patterns, e.g. Urianger) to start with a dialogue outline written more casually that summarizes what you want him to say, then focus on editing and chewing that thesaurus in a later pass through your work.

One stumbling block people run into is taking “Zenos is verbose/yaps a lot” to mean “every one of his sentences should be very long,” but he has plenty of snappy short sentences mixed in with his speech patterns as well.