Jeju (Jeju: ; Jeju RR: , or , or ), often called Jejueo or Jejuan in English-language scholarship, is a Koreanic language originally from Jeju Island, South Korea. It is not mutually intelligible with mainland Korean dialects. While it was historically considered a divergent Jeju dialect of the Korean language, it is increasingly referred to as a language. It is declining in usage, and was classified by UNESCO in 2010 as critically endangered, the highest level of language endangerment possible. Revitalization efforts are ongoing.
The consonants of Jeju are similar to those of Seoul Korean, but Jeju has a larger and more conservative vowel inventory. Jeju is a head-final, agglutinative, suffixing language like Korean. Nouns are followed by particles that may function as case markers. Verbs inflect for tense, aspect, mood, evidentiality, relative social status, formality, and other grammatical information. Korean and Jeju differ significantly in their verbal paradigms. For instance, the continuative aspect marker of Jeju and the mood or aspect distinction of many Jeju connective suffixes are absent in Korean. Most of the Jeju lexicon is Koreanic, and the language preserves many Middle Korean words now lost in Standard Korean. Jeju may also have a Peninsular Japonic substratum, but this argument has been disputed.
Jeju was already divergent from the Seoul dialect of Korean by the fifteenth century and unintelligible to mainland Korean visitors by the sixteenth century. The language was severely undermined by the Jeju uprising of 1948, the Korean War, and the modernization of South Korea. All fluent speakers remaining in Jeju Island are now over seventy years old. Most people in Jeju Island now speak a variety of Korean with a Jeju substratum. The language may be somewhat more vigorous in a diaspora community in Osaka, Japan, as many Jeju people migrated to Osaka in the 1920s, but even there, younger members of the community tend to speak Japanese.
Nomenclature and relationship to Korean
Various terms in both Korean and English exist for the Jeju language, which also vary depending on whether it is considered a separate language or a dialect of Korean by the speaker.
Among native speakers, the term "Jeju speech" () is most commonly used. In English-language scholarship, it is often called Jejueo or Jejuan.
Language or dialect distinction
Jeju is closely related to Korean. It was traditionally considered an especially divergent dialect of Korean, and is still referred to as such by the National Institute of the Korean Language and the South Korean Ministry of Education.
Until the 2000s, South Korean academia preferred the term "Jeju dialect" (). While the term "Jeju language" () was first used in 1947, it was not until the mid-1990s that the term gained traction. The majority of South Korean academic publications switched to using "Jeju language" by the early 2010s. Since somewhat earlier, "Jeju language" has also been the term preferred in local law, such as the 2007 Language Act for the Preservation and Promotion of the Jeju Language, and by non-governmental organizations working to preserve the language. The only English-language monograph on Jeju, published in 2019, consistently refers to it as a language as well.
Mutual intelligibility with modern South Korean
Jeju is not mutually intelligible with even the southernmost dialects of South Korea. In a 2014 survey measuring intelligibility, Korean speakers from three different dialect zones (Seoul, Busan, and Yeosu) were exposed to one minute of spoken Jeju, with a control group of native Jeju speakers. On average, South Korean native speakers from all three dialect zones answered less than 10% of the basic comprehension questions correctly, while native Jeju speakers answered over 89% of the questions correctly. These results are comparable to the results of an intelligibility test of Norwegian for native Dutch speakers. Diaspora Jeju speakers living in Japan have also reported that they find it difficult to understand South Korean news media, and resort to Japanese subtitles when watching South Korean TV shows.
Geographic distribution
Jeju was traditionally spoken throughout Jeju Province except in the Chuja Islands, halfway between Jeju Island and mainland Korea, where a variety of Southwestern Korean is found. The language is also used by some of the first- and second-generation members of the Zainichi Korean community in Ikuno-ku, Osaka, Japan.