I just learned of the (hypothetical) existence of the (alleged) language Koguryo (or Goguryeo), perhaps spoken in the first millenium C.E. around the Korean/Chinese border. The LINGUIST List description says:
A possible language once spoken in NE China (Liaoning), Manchuria, and Korea, 1st century to mid-8th century A.D. The earliest solid historical reference to the Koguryo people (1st century A.D.) has them in the Liao-hsi area (now part of Liaoning province, northeast of Tientsin) of China. The evidence for this language lies almost solely in toponyms rather than texts, and is thus unreliable. The Archaic Koguryo corpus dates to the third and fourth century A.D. and consists of about a dozen identifiable lexemes recorded in Chinese historical and geographical accounts of the Koguryo kingdom. The Old Koguryo corpus, largely dating to the seventh and eighth centuries, consists of over a hundred lexemes found in the form of glossed toponyms, plus a small number of words recorded in Chinese historical and geographical accounts. The language, if real, may be related to Japanese…
(Via T. Carter at Lifechanges … Delayed.)
One of the tantalizing and frustrating things about this kind of study is that you know there’s a right answer, and you even have some hints as to what it might be, but you also are aware that the evidence you need probably doesn’t exist anywhere in the actual world. Cf. Pictish, Etruscan, Hunnish, etc.
But wait! The Pictish archive has just been unearthed! Hundreds of pages of chronicles and epic poetry…..
No, it didn’t happen.
There has been some discussion of this on the Korean Studies List @ http://www.koreaweb.ws/ks . See archives for Dec 2003 and Jan 2004.
It’s now got a fairly comprehensive Wikipedia page.