(KGT 141f.):  A name for the inhabitant of a planet (and, therefore, the name of a race of beings) is formed by adding ngan (inhabitant) to the planet name (excluding the number, if any): lIghonngan (Ligonian), tera'ngan (Earther, Terran), romuluSngan (Romulan). (Actually, there is some phonetic variation here. Ligonian is often pronounced lIghongan, dropping the final n of lIghon before the initial ng of ngan. This is not considered an error, only an alternate pronunciation.) Occasionally, and no doubt owing to influence from Federation Standard, from which names, as noted, are often taken, an extra syllable, -ya'-, comes between the planet name and ngan. Thus, Denebian - that is, an inhabitant of one of the Deneb planets - is both DenIbngan and DenIbya'ngan. The planet name itself is also heard in two forms: DenIb (formed from the name Deneb) and DenIbya' (formed by dropping the ngan from DenIbya'ngan).

(MO to Lieven, 3/27/2012):  Maltz said that for language names the construction "country + Hol" is most common (so he preferred DoyIchlan Hol). Of course, it doesn't have to be a "country." It could be a region or a political unit or alliance of another kind (which is why DIvI' Hol fits in). He noted that tlhIngan Hol is really a shortened form of tlhIngan wo' Hol, but nobody ever says that in everyday speech. If one were to say vulqangan Hol ("Vulcan's language" or "Vulcans' language"), that could mean the same thing as vulqan Hol, so the speaker would generally not be misunderstood, but if at an intergalactic gathering a Vulcan were speaking Federation Standard, then vulqangan Hol for that Vulcan at that time and place would be DIvI' Hol. There is no such thing as qa'naDa' Hol, but qa'naDa'ngan Hol might refer to DIvI' Hol or vIraS Hol (or Cree or Inuit or many other languages). So Maltz thought it best to avoid the -ngan construction for language names.

See for example romuluS HIq "Romulan ale" (i.e. the famous potent alcoholic beverage associated with Romulus which is banned in the Federation) vs. romuluSngan HIq "the Romulan's ale (e.g. the drink of that Romulan at the end of the bar).

SEE ALSO:

toq             be inhabited (v)
chIm            be uninhabited, be deserted (v)

roghvaH         population (n)
ngan            inhabitant (n)
Sung            native (n)
nov             alien, outsider, foreigner (n)