decade of the 2000s, the majority of South Korean academic publications had switched to the term "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. Among native speakers, the term Jeju-mal "Jeju speech" is most common. Jeju is not mutually intelligible with even the southernmost dialects of mainland Modern Korean. In a 2014 test for 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, 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 also report 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. Compared to mainland Korean dialect groups, there is little internal variation within Jeju. A distinction between a northern and southern dialect with a geographic divide at Hallasan is sometimes posited, but an eastern-western dialectal divide cutting through Jeju City and Seogwipo may better explain the few dialectal differences that do exist. A 2010 survey of regional variation in 305 word sets suggests that the north–south divide and the east–west divide coexist, resulting in four distinct dialect groups. History and decline The Koreanic languages are likely not native to Jeju Island; it has been proposed that the family has its roots in Manchuria, a historical region in northeastern Asia. It is thought that Koreanic speakers migrated from southern Manchuria between the third and eighth centuries CE. Linguist Alexander Vovin suggests that the ancient kingdom