A five-level pitch system
The dialect of the Yaeyama language spoken on Hateruma Island is a member of the Japonic language family, but it is not mutually intelligible with standard Japanese. A primary reason is its use of pitch. While standard Japanese uses a pitch-accent system to distinguish some words, the Hateruma dialect has a full tonal system where the meaning of a word can depend entirely on its melodic contour.
Linguists have identified three main accent patterns in the dialect: falling, level, and rising. These patterns, which must be applied correctly to be understood, are constructed from a system of five distinct pitch levels. This gives the language a phonetic complexity not in mainland Japanese. This system is distinct from other Ryukyuan languages, which may have simpler pitch systems or have lost tonal distinctions found in Hateruma. The dialect of Hateruma is also spoken in the village of Shiraho on nearby Ishigaki island, a result of forced migrations in the 18th century.
A unique phonological island
The Hateruma dialect is classified as an innovative branch of the Yaeyama language group. Its phonology contains several features not found in other Japonic varieties. The dialect has a seven-vowel system, whereas standard Japanese uses five. One of these is a pharyngealized vowel, written as eˤ, a sound produced with constriction in the throat that is unique among all languages of the Ryukyu Islands.
Another distinctive feature is its strong aspiration of initial voiceless consonants. This puff of air is so strong that it often causes the following sound to become voiceless. Hateruma is the only Yaeyama dialect where this effect is strong enough to devoice nasal and liquid consonants, such as 'm' or 'r'. Despite these innovations, the dialect is also conservative. It preserves certain phonetic distinctions that show the syllable structure of Old Japanese, which have since merged and disappeared in all other Japonic languages. The broader Yaeyama language, including the Hateruma dialect, is classified by UNESCO as "severely endangered". Most speakers are over the age of 60, and the language is rarely used in daily life by younger generations.