Mark Liberman has a Language Log post about an oddly formed adjective that’s always pleased and puzzled me, Shanghainese. Where does that intrusive -n- come from? I assumed it had something to do with Chinese, but Mark provides more parallels:
But my guess is that this starts with the analogical shadow cast by the place names ending in ‘n’—Japan, Taiwan, Canton, Bhutan—whose adjectival forms (and the corresponding language names and/or ethnonyms) add ‘-ese’—Japanese, Taiwanese, Cantonese, Bhutanese. Then there are the cases where a final syllable is elided in the place names to get adjectival forms that happen to end up ending in ‘-nese’: Chinese, Lebanese.
Finally—and most relevantly—there are some long-established cases where there is an intrusive ‘n’: Java → Javanese, Sunda → Sundanese, Bali → Balinese, etc. The oldest of these seems to be Javanese, which the OED traces back to 1704[...] and which may derive from an earlier Javan…
The preference for -ese as the adjectival ending for places in the “East Indies” presumably reflects the influence of Dutch, which also (I think) regularly has intrusive -n- in such words: Javanees, Sundanees, Balinees, etc. I don’t have access to a historical dictionary of Dutch—is there one?—but I assume that these words date back at least to the early 17th century, if not the 16th. I also don’t know whether the use of intrusive -n- to repair hiatus is the general pattern in Dutch, or whether (as in English) it’s just one of many quasi-regular local options.
He expressed surprise that the OED’s earliest citation for the word Vietnamese is from 1947; I reminded him (via e-mail, LL having no comments) that “until WWII and Ho’s independence movement, there was no such thing as Vietnam—what we think of as Vietnam was three provinces of French Indochina, and you’d use Tonkinese, Annamese/Annamite (interesting that there was no settled form), or Cochin-Chinese as called for.” And I added the following observation, which I repeat here as perhaps of interest to such of my readers as are interested in recondite geographical terminology: