Rick: “Splittist” is certainly an ugly term. It’s communist-speak: My immense and comprehensive 1977 Far East English-Chinese Dictionary (from Taiwan) doesn’t have it, but my smaller New China Dictionary (mainland, same year) does. I think it’s just the kind of thing you get when low-paid translators have to render yards and yards of mind-numbing political jargon into another language.
Chinese suffixes like “-ist,” “-ism,” and “-ology” are freer-floating than the English equivalents. A scholar once introduced himself to me as a “Red-ologist” (hong-xue-jia). What the heck was that, I wondered. Turned out he was one of the world’s leading authorities on the great 18th-century classic novel Red Chamber Dream. So when you’re translating the latest 8,000-word editorial from People’s Daily, and it’s close to quittin’ time, and you’re dying for a smoke, and the other guy’s using the Chinese-English dictionary, and you hit a Chinese word made of “split” and “-ist,” you’re going to write “splittist” and press on to the end of your workload. It ends up on the Reuters wire, and a barbarous usage is born.
I’m not totally sure there isn’t a case for it. It has the dogmatic blustering color of CCP-speak, and it’s useful to have that poked in our eyes now and then. If they put out their propaganda materials in the soothing language of a corporate annual report, we’d be tempted not to mind them so much. And really, none of the alternatives you mentioned is congruent in Chinese. “Secede” for example, goes into Chinese with more of a flavor of “shucking off” or “escaping from,” which of course is not at all what the CCP wants us to think about Tibetan nationalists.