Uchināguchi, or the Okinawan “dialect”, is a language spoken in Okinawa Island and nearby islands. Although it is called a dialect, it is unintelligible to speakers of mainland Japanese. Uchināguchi is commonly associated with the dialects spoken in Central Okinawa and surrounding regions however some may classify dialects spoken on other islands such as Miyako-jima, to be a member of Uchināguchi.

The Shuri dialect of Uchināguchi is the most influential variant of the Ryukyuan languages due to its location as the capital of the Ryukyu Kingdom as well as containing the largest population center in the Ryukyuan Islands. Within the Ryukyuan languages, the Shuri dialect is clustered within the Amami-Okinawan branch along with the Amami, Kunigami, and Yoron dialects. In the south, Miyako, Yaeyama, and Yonaguni dialects form the Sakishima branch of the Ryukyuan languages.

While there are some similarities between Uchināguchi within the same branches, there are many differences. Intelligibility between the Amami-Okinawan branch and the Sakishima branch is very low. The Amami-Okinawan branch itself is split into northern and southern groups, with intelligibility between them also being low. Despite this, the languages of the Ryukyu Islands still show strong similarities with each other, as well as to the Japanese language. It is believed that Proto-Japanese, split around the 7th century and developed into what is now the Japanese and Ryukyuan languages. It is also said that the Ryukyuan languages preserve many aspects of ancient Japanese that is no longer found in modern Japanese, such as the use of “F” sound which has been replaced by “H” in modern Japanese.

Today, standard Japanese is primarily spoken in the Okinawa Prefecture, however many of the older generation in Okinawa are still able to converse in Uchināguchi. Those who are unable to speak Uchināguchi as well as non-Okinawans living in the prefecture are still familiar with some of the more basic and common Uchināguchi phrases. Reasons for the deterioration of use of the Uchināguchi language stem from earlier Japanese government policies which forbade its use. In particular, the language ban was so severe that during the Battle of Okinawa, anyone caught speaking Uchināguchi were considered as traitors and executed.

Further Reading:
Ethnologue report on Japanese languages
Okinawa Shorinryu's site on Uchinaguchi
Japan Policy Research Institute article on assimilation policies in Okinawa