Northwest Okinawa; north Amami-Oshima island.
Naze, Sani. Inherent intelligibility generally impossible, or very difficult, with Ryukyuan languages and Japanese [jpn].
Adults only. The younger the generation, the more fluently they speak Japanese [jpn] (Wurm and Hattori 1981). Those under 20 mostly monolingual in Japanese (1989 T. Fukuda).