If your language is not and never has been written, and you decide to start writing it, you have a few options. One is to wait for someone to invent an alphabet (or set of signs) for your language. A second option is to wait for some missionaries or conquerors to apply their alphabet (or set of signs) to your language. A third option is to create your own alphabet (or set of signs). Finally, a fourth option to voluntarily (or semi-voluntarily) adopt someone else's alphabet (or set of signs).
Recently a minority tribe (consisting of about 60,000 people) centered in the Indonesian city of Bau-Bau decided that the perfect script with which to capture their language was . . . Hangul, better known as Korean. While it may be that the Korean alphabet (and yes, Korean uses an alphabet) perfectly captures the sounds of Cia-cia, it is still an odd choice for a number of reasons. First, Hangul is not used for any language other than Korean, and is not "official" anywhere outside of the Korean penninsula. Second, none of Bau-Bau's neighbors use Hangul to write. That seems obvious from point one, but remember that it also means that literacy in Cia-cia and another language will require literacy in multiple alphabets. It also means relatively few people will be willing or able to learn written Cia-cia. Third, there is no historical, cultural, or other tie between this tribe and Korea. It was more or less chosen out of the blue.
Meanwhile, Korean perspective on this is interesting too. A Korean institute actually markets the use of Hangul internationally, and they are supplying books and a Korean center in Bau-Bau. The Yonhap article linked above talks about linguists hoping this will help spread Hangul globally, and allow a demonstration of the "excellence" of Hangul worldwide. So, part of this is national pride for Korea. A more tenuous note comes from Kim Joo-won, who is quoted as saying "in the long run, the spread of Hangeul will also help enhance Korea's economy as it will activate exchanges with societies that use the language."
I'm not sure the Koreans have thought the economic/societal exchange issue through. I mean, written Vietnamese uses an adapted Latin alphabet, and is part of the eastern Mon-Khmer language family. The missionaries who adapted the Latin alphabet to Vietnamese were Portuguese and (presumably) spoke Portuguese. Portuguese uses the Latin alphabet and is part of the Iberico-Romance branch of the Romance languages. I don't think the common alphabet has sparked an economic boon between these countries. Similarly, Korean is a linguistic isolate (!), while Cia-cia is on Malayo-Polynesian branch of the Austronesian languages. In other words, not so related.
In any case, it is very interesting that this decision was made. It will be interesting to see if the alphabet is maintained if Korean support wanes, and whether closer relations do materialize.