(covers information from several alternate timelines)
This page contains information regarding Star Trek: Picard, and thus may contain spoilers.
The Romulan language was used within the Romulan Star Empire. Its written form consists of square and rectangular letters, which could be arranged horizontally or vertically. (e.g., TNG: "The Mind's Eye", "Face of the Enemy"; DS9: "Inter Arma Enim Silent Leges"; Star Trek Nemesis)
Upon the first official encounter between Romulans and Starfleet in 2152, audio-only communications were established. Although the early universal translator initially had problems to lock on to the Romulan language, Enterprise communications officer Hoshi Sato was able to translate what turned out to be an ultimatum to depart immediately. (ENT: "Minefield")
In 2370, Jean-Luc Picard identified an artifact recovered from Calder II as being from Vulcan, because the alphabet and symbology of the glyphs and pictograms on the artifact was much more consistent with early Vulcan than Romulan. (TNG: "Gambit, Part II")
Words and phrasesEdit
- Chula: Place name of a valley on Romulus (TNG: "The Defector")
- D'deridex: "Warbird", a term designating Romulan starships:
- Gal Gath'thong: A place name on Romulus (TNG: "The Defector")
- Ganmadan: Ancient term for the "Day of Annihilation" (PIC: "Absolute Candor")
- Jolan tru: A salutation used for "hello" and "goodbye" (TNG: "Unification I"; ENT: "United"; PIC: "Absolute Candor")
- Kali-fal: A type of Romulan ale (DS9: "In the Pale Moonlight")
- Pixmit: Cards with cultural significance (PIC: "The End is the Beginning")
- Prod: Praetor or commander (Star Trek)
- Qalankhkai: "Freeblade", a Qowat Milat warrior bound to a worthy cause (PIC: "Absolute Candor")
- Qezhtihn: An insult (PIC: "The End is the Beginning")
- Qowat Milat: An order of warrior nuns (PIC: "Absolute Candor")
- Shaipouin: "False door" (PIC: "The End is the Beginning")
- Tal Shiar: The Romulan intelligence agency/secret police (TNG: "Unification I")
- Tan qalanq: A sword wielded by the Qowat Milat (PIC: "Absolute Candor")
- Uhlan: A rank in the Romulan military (TNG: "The Defector")
- Veruul: A Romulan insult, analogous to the Klingon word "pahtak" (petaQ); possibly profane
- Viinerine: A type of food (TNG: "Face of the Enemy")
- Vorta Vor: The source of all creation (Star Trek V: The Final Frontier)
- Zhat Vash: A term sometimes used for the dead (PIC: "Maps and Legends")
- Uhn kan'aganna! Tehca zuhn ruga'noktan!
- Uhn Kan'aganna! Tehca zuhn! Neemasta kan'aganna uckwazta!
- Kuhn'ukchtacht zuhn vockwadai!
- Bar'ak t'stu annankana. (ENT: "Minefield")
Background information Edit
Romulan dialogue was spoken by Ayel (played by Clifton Collins, Jr.) in a deleted scene from the film Star Trek. Translated into English, the Romulan he said meant, "Commander Nero. We're surrounded. What are your orders?" The Romulan dialogue written for the show was supplied by Marc Okrand, better known for creating Klingonese. "I had never done anything with Romulan before, but since Romulans and Vulcans are related, I made the Romulan language one that could be related to Vulcan – not closely, but in certain patterned ways. The two languages are heard mostly in the background as opposed to being spoken by main characters." 
For Star Trek: Picard, constructed language creator Trent Pehrson was hired to develop the grammar and vocabulary of Romulan language spoken in the series. Pehrson also served as a dialect coach for the language.  "I was given instruction on what preexisting fragments were to be considered as canon. I incorporated all of those. Essentially, those really only yielded limited phonotactic information, some vague lexical items, and a hand-full of possible grammatical morphemes. There was also some Vulcan canon, which was useful, in a historical linguistic sense, to further flesh out phonotactics, and to derive another small set of lexical items. Native Romulan orthography fragments, used in prior canon production, were aesthetically pleasing, but were clearly just a thinly disguised version of the Roman alphabet. So, I used only the visual aesthetic from that, and created a system fitting to the actual phonotactics and phonemic inventory of the Romulan language. ST:Picard, E2 recently featured a decent sampling in a scene. The rest (the majority of the language) I had to construct." 
- In Diane Duane's novel The Romulan Way, the Romulan language is said to be related to the Vulcan language. This suggests that during the Exodus of the Romulans, they abandoned most things Vulcan. "One thing they agreed on quickly was that they could not stop being Vulcan while they still spoke the language." In order to rectify this problem, the Romulans went back to old or "High" Vulcan and "aged" the language in another direction. The resulting tongue was named Rihan, with the Romulans' name for themselves being Rihannsu in Duane's novels, meaning "the Declared", in reference to their decision to secede from Vulcan society. (This name also used to collectively refer to the novel series.) The Romulan Way includes a partial glossary for the language (reprinted in the omnibus edition Rihannsu: The Bloodwing Voyages), and Duane reportedly intended to publish a Rihan counterpart to The Klingon Dictionary but it never materialized. However, fandom has extensively expanded on it, and it has been reused in other licensed works including the Romulan War series of Star Trek: Enterprise novels and Star Trek Online.
- In the novel Vulcan's Heart, Spock notices Romulans cursing in old Vulcan.
- The Romulan language font is called Kzhad, and was created by Monte Thrasher based on the shapes of LED displays.
- FASA gaming manuals referred to the Romulan word for the Romulan language as "Romlastha".