That establishes very clearly, both in script background and in dialogue, that the Romulan Praetor is the head of government.
Only in script background, which doesn't count. There's nothing in the dialogue to establish the Praetor as the supreme leader.
And if that's not enough, the next time we encounter a Romulan Praetor -- two of them, actually, one after another -- it's Hiren and then Shinzon. Both are very clearly the leaders of the Romulan Star Empire.
Hiren is present at (and possibly presiding over) a Senate meeting. The only way he demonstrates leadership is by repeating the government's official position on matters Reman, which is something the lowliest underling could do; apart from that, he's the one who calls in security, which is also something the lowliest court servant would be tasked with doing. Not "clear leader" at all.
Shinzon could lead as warlord and be rightly addressed as Praetor, just like a dictator on Earth could be addressed as General even though this is not a formally acceptable title for the leader of the republic or "republic" he is ruling over.
Just pointing out that we're still at full liberty to interpret the Romulan system as a very close analogy to the Roman one, no matter what the writers may have been thinking, because they didn't put all of that thinking on writing "clearly enough".
You are utterly misremembering "Inter Arma," as I demonstrated above.
True. The background on Neral comes from "Unification" instead, and establishes that character as having started out as a venerable Proconsul and despite this apparently having proceeded with Praetorial ambitions, a seeming step down in status.
Makes sense for somebody with a lifespan of several centuries, though. After becoming Consul and retiring as Proconsul, Neral would have attained all; the civilization wouldn't wish for him to immediately re-attain Consul status, but might benefit from offering it to him again at a later date, after he has once again demonstrated his capabilities as a militant Praetor.
Let's note, though, that the Neral in "Inter Arma" need not be the same character as the Neral in "Unification". The two are played by different actors who don't resemble each other much, not even if counting in a few years of aging (for a species that doesn't visibly age much in a century!). The latter Neral doesn't mention any of the background of the former. We could easily be seeing two members of the same family, one with greater political success ("Unification"), one still striving at an older age ("Inter Arma").
The only canonical reference to Romulan royalty is the reference to a Romulan Empress as one of Q's potential mates in "The Q and the Grey." There is, however, no evidence whatsoever that Q "erased her from history," and the relative dearth of canonical information on the Romulan Emperors is consistent with the mostly ceremonial role postulated for them in the novels.
True. OTOH, it's equally consistent with the complete absence of an Emperor from the modern Romulan political system.
Arbitrary translation traditions are hardly unheard of in history.
The reason to shun arbitrariness does not stem from the few aberrations we see - it stems from the systematic nature of the bulk of the evidence. If only Cardassian and Ferengi militaries get ranks differing from USN ones, then we obviously would like to have an explanation for these lone aberrations.
To be sure, Star Trek tends to give political entities unique names, apparently for the sheer heck of it: Cardassian UNION, Ferengi ALLIANCE, Breen CONFEDERACY, Olivet QUANGO... If the UT or other linguistic authority is this specific with the nature of these political entities, then we should probably assume it's being pedantically accurate with Klingon EMPIRE and Romulan EMPIRE as well.
Or then "Empire" is a generic expression for a political entity that has imperialistic leanings, regardless of the type of government. After all, nobody ever bothered to stop calling the Klingons an EMPIRE despite the knowledge that there was no Emperor. The same could very well hold for the Romulans, a potential imperialistic republic.
And there's no reason to think that that vocabulary is automatically chosen by the UT program.
Save for the already mentioned "troglyte" thing...
Not to mention that our heroes often run into previously unknown aliens, at which point the UT provides them with a fluent translation, complete with complex idioms and weird terminology - without ever consulting our heroes on the choice of words.
On the Romulan/Romalin issue, we might assume that Sato heard a specific grammatic derivation of the root word Romulan, and T'Pol pointed out to her that Romulan was the actual root word and the one that should be used in the given English context. However, it might be that Romalin is the modern Romulan pronunciation, yet T'Pol refuses to use this form and insists on the original, historically established one: "Ignore them; that's no 'National Front of Pure Space'. It's pronounced 'Space Nazis'."
Timo Saloniemi