...Perhaps explored by valiant Vulcan, Andorian and Tellarite Starfleet crews, respectively?
Diane Duane goes the route where Romulus and Remus are named for their twinness by passing Earthlings, while ENT establishes that "Romulan" is an English spelling for a Vulcan version of the native name; in both cases, all the rest is frivolous embellishment on the Romulan theme, probably by the ever-mischievous Universal Translator. Which one is the more appealing origin story? I'm partial towards the latter, really, as twin worlds should be common enough in the Trek universe (Earth is one, Vulcan apparently is one), and "Romulus/Remus" should have been used up long before the flight of the Carrizal.
Both stories can be true simultaneously, of course: we know that knews traveled slowly back then, and the heroes of the Carrizal may have failed to influence the establishing of the Vulcan name "Romulans", or be influenced by it, while hitting coincidental paydirt. Heck, the UT may have subtly aided the Carrizal folks in their choice of "Romulus/Remus" over "Serena/Venus"...
Deciding that Earth words cannot be native alien names is futile anyway: there are far too many Earth words to choose from, covering all the bases already. Similarly, there is no shortage of "coincidences" in this universe when we decide on zero limiting parameters on what "counts": planet "Vulcan" may happen to have volcanoes, but is otherwise short on things tying it to Roman gods of note, British Cold War bombers, or whatever else we might want to find a connection with. It suffices to score a single random hit out of the zillions available.
Timo Saloniemi