During my dissertation fieldwork in Papua New Guinea over thirty years ago, I discovered that a bunch of Austronesian languages in Morobe Province mark their relative clauses in a manner that is pretty rare from a typological point of view: they mark both the beginning and the end of the clauses. An English equivalent would go something like, “The language [that they were speaking that] sounded vaguely familiar,” or “The language [which they were speaking such] sounded vaguely familiar.”
The only other place where I could find languages that did the same was in Central Africa, and my dissertation cited a 1976 article by the great French linguist Claude Hagège which mentioned by name two Nilo-Saharan languages, Moru and Mangbetu, and two Niger-Congo languages, Mbum and M’baka. Over the years, I lost track of anything pertaining to those languages except their names.
But recently his interest revived and he thought to ask his brother, who “had spent years working in the (at that time) Central African Empire for the US Peace Corps and USAID while I was writing my dissertation in linguistics,” and his brother asked “his linguist friend Raymond Boyd at CNRS whether he could think of Adamawa-Ubangi languages that used such markers for relative clauses,” and Boyd responded “Right off, I can’t think of one that DOESN’T.” Read Joel’s post for examples of this interesting phenomenon.