The Old Yue language is an unclassified language or set of languages spoken in the state of Yue during the Eastern Zhou dynasty. It may also refer broadly to the languages spoken by Yue peoples in any of the Yue polities in southern China and northern Vietnam c. 700 BCE – c. 100 BCE.

Knowledge of Yue speech is limited to fragmentary references and possible loanwords in Sinitic languages. The longest attestation is the Song of the Yue Boatman, a short song transcribed phonetically in Chinese characters in 528 BC and included, with a Chinese translation, in the Garden of Stories compiled by Liu Xiang five centuries later. Scholars disagree about which languages the Yue spoke, and draw candidates from the non-Sinitic language families still represented in areas of southern China.

Classification theories Candidates for the Old Yue language include Kra–Dai, Hmong–Mien, and Austroasiatic languages. Chinese, Kra–Dai, Hmong–Mien, and the Vietic branch of Austroasiatic have similar tone systems, syllable structure, grammatical features and lack of inflection, but these features are believed to have spread by means of diffusion across the Mainland Southeast Asia linguistic area, rather than indicating common descent. Scholars in China often assume that the Yue spoke an early form of Kra–Dai. According to Sagart (2008), this is far from self-evident, because the core of the Kra–Dai area geographically is located in Hainan and the China–Vietnam border region, which is beyond the extreme southern end of the Yue area. The linguist Wei Qingwen gave a rendering of the "Song of the Yue boatman" in Standard Zhuang. Zhengzhang Shangfang proposed an interpretation of the song in written Thai (dating from the late 13th century) as the closest available approximation to the original language, but his interpretation remains controversial. Peiros (2011) shows with his analysis that the homeland of Austroasiatic is somewhere near the Yangtze. He suggests southern Sichuan or slightly west from it, as the likely homeland of proto-Austroasiatic speakers before they migrated to other parts of China and then into Southeast Asia. He further suggests that the family must be as old as proto-Austronesian and proto-Sino-Tibetan or even older. The linguists Sagart (2011) and Bellwood (2013) support the theory of an origin of Austroasiatic along the Yangtze river in southern China. Sagart (2008) suggests that the Old Yue language, together with the proto-Austronesian language, was descended from the language or languages of the Tánshíshān‑Xītóu culture complex (modern-day Fujian province of China), making the Old Yue language a sister language to proto-Austronesian, which Sagart sees as the origin of the Kra–Dai languages.

Behr (2009) also notes that the Chǔ dialect of Old Chinese was influenced by several substrata, predominantly Kra-Dai, but also possibly Austroasiatic, Austronesian and Hmong-Mien.Behr, Wolfgang (2009). "Dialects, diachrony, diglossia or all three? Tomb text glimpses into the language(s) of Chǔ", TTW-3, Zürich, 26.-29.VI.2009, "Genius loci".

Kra–Dai arguments The proto-Kra–Dai language has been hypothesized to originate in the Lower Yangtze valleys. Ancient Chinese texts refer to non-Sinitic languages spoken across this substantial region and their speakers as "Yue". Although those languages are extinct, traces of their existence could be found in unearthed inscriptional materials, ancient Chinese historical texts and non-Han substrata in various Southern Chinese dialects. Thai, one of the Tai languages and the most-spoken language in the Kra–Dai language family, has been used extensively in historical-comparative linguistics to identify the origins of language(s) spoken in the ancient region of South China. One of the very few direct records of non-Sinitic speech in pre-Qin and Han times having been preserved so far is the "Song of the Yue Boatman" (Yueren Ge 越人歌), which was transcribed phonetically in Chinese characters in 528 BC, and found in the 善说 Shanshuo chapter of the Shuoyuan 说苑 or 'Garden of Persuasions'.

Willeam Meacham (1996) reports that Chinese linguists have shown strong evidence of Tai vestiges in former Yue areas: Lin (1990) found Tai elements in some Min dialects, Zhenzhang (1990) has proposed Tai etymologies and interpretations for certain place names in the former states of Wu and Yue, and Wei (1982) found similarities in the words, combinations and rhyming scheme between the "Song of the Yue Boatman" and the Kam–Tai languages.

James R. Chamberlain (2016) proposes that the Kra-Dai language family was formed as early as the 12th century BCE in the middle of the Yangtze basin, coinciding roughly with the establishment of the Chu state and the beginning of the Zhou dynasty. Following the southward migrations of Kra and Hlai (Rei/Li) peoples around the 8th century BCE, the Yue (Be-Tai people) started to break away and move to the east coast in the present-day Zhejiang province, in the 6th century BCE, forming the state of Yue and conquering the state of Wu shortly thereafter. According to Chamberlain, Yue people (Be-Tai) began to migrate southwards along the east coast of China to what are now Guangxi, Guizhou and northern Vietnam, after Yue was conquered by Chu around 333 BCE. There the Yue (Be-Tai) formed the polities Xi Ou, which became the Northern Tai and the Luo Yue, which became the Central-Southwestern Tai. However, Pittayaporn (2014), after examining layers of Chinese loanwords in proto-Southwestern Tai and other historical evidence, proposes that the southwestward migration of southwestern Tai-speaking tribes from the modern Guangxi to the mainland of Southeast Asia must have taken place only sometime between the 8th–10th centuries CE, long after 44 CE, when Chinese sources last mentioned Luo Yue in the Red River Delta.

Ancient textual evidence In the early 1980s, Zhuang linguist, Wei Qingwen (韦庆稳), electrified the scholarly community in Guangxi by identifying the language in the "Song of the Yue Boatman" as a language ancestral to Zhuang. Wei used reconstructed Old Chinese for the characters and discovered that the resulting vocabulary showed strong resemblance to modern Zhuang. Later, Zhengzhang Shangfang (1991) followed Wei’s insight but used Thai script for comparison, since this orthography dates from the 13th century and preserves archaisms relative to the modern pronunciation. Zhengzhang notes that 'evening, night, dark' bears the C tone in Wuming Zhuang xamC2 and ɣamC2 'night'. The item raa normally means 'we inclusive' but in some places, e.g. Tai Lue and White Tai 'I'. However, Laurent Sagart criticizes Zhengzhang's interpretation as anachronistic, because however archaic that Thai script is, Thai language was only written 2000 years after the song had been recorded; even if the Proto-Kam-Tai might have emerged by 6th century BCE, its pronunciation would have been substantially different from Thai. The following is a simplified interpretation of the "Song of the Yue Boatman" by Zhengzhang Shangfang quoted by David Holm (2013) with Thai script and Chinese glosses being omitted:The upper row represents the original text, the next row the Old Chinese pronunciation, the third a transcription of written Thai, and the fourth line English glosses. Finally, there is Zhengzhang's English translation.

Some scattered non-Sinitic words found in the two ancient Chinese fictional texts, the Mu Tianzi Zhuan () (4th c. B.C.) and the Yuejue shu () (1st c. A.D.), can be compared to lexical items in Kra-Dai languages. These two texts are only preserved in corrupt versions and share a rather convoluted editorial history. Wolfgang Behr (2002) makes an attempt to identify the origins of those words:

"吳謂善「伊」, 謂稻道「緩」, 號從中國, 名從主人。"

“The Wú say yī for ‘good’ and huăn for ‘way’, i.e. in their titles they follow the central kingdoms, but in their names they follow their own lords.”

伊 yī < ʔjij < *bq(l)ij ← Siamese diiA1, Longzhou dai1, Bo'ai nii1 Daiya li1, Sipsongpanna di1, Dehong li6 < proto-Tai *ʔdɛiA1 | Sui ʔdaai1, Kam laai1, Maonan ʔdaai1, Mak ʔdaai6 < proto-Kam-Sui/proto-Kam-Tai *ʔdaai1 'good' || proto-Malayo-Polynesian *bait

緩 [huăn] < hwanX < *awan ← Siamese honA1, Bo'ai hɔn1, Dioi thon1 < proto-Tai *xronA1| Sui khwən1-i, Kam khwən1, Maonan khun1-i, Mulam khwən1-i < proto-Kam-Sui *khwən1 'road, way' | proto-Hlai *kuun1 || proto-Austronesian *Zalan (Thurgood 1994:353)

yuè jué shū 越絕書 (The Book of Yuè Records), 1st c. A.D.

絕 jué < dzjwet < *bdzot ← Siamese codD1 'to record, mark' (Zhengzhang Shangfang 1999:8)

"姑中山者越銅官之山也, 越人謂之銅, 「姑[沽]瀆」。"

“The Middle mountains of Gū are the mountains of the Yuè’s bronze office, the Yuè people call them ‘Bronze gū[gū]dú.”

「姑[沽]瀆」 gūdú < ku=duwk < *aka=alok

← Siamese kʰauA1 'horn', Daiya xau5, Sipsongpanna xau1, Dehong xau1, Lü xău1, Dioi kaou1 'mountain, hill' < proto-Tai *kʰauA2; Siamese luukD2l 'classifier for mountains', Siamese kʰauA1-luukD2l 'mountain' || cf. OC 谷 gǔ < kuwk << *ak-lok/luwk < *akə-lok/yowk < *blok 'valley'

"越人謂船爲「須盧」。"

"... The Yuè people call a boat xūlú. (‘beard’ & ‘cottage’)"

須 xū < sju < *bs(n)o

? ← Siamese saʔ 'noun prefix'

盧 lú < lu < *bra

← Siamese rɯaA2, Longzhou lɯɯ2, Bo'ai luu2, Daiya hə2, Dehong hə2 'boat' < proto-Tai *drɯ[a,o] | Sui lwa1/ʔda1, Kam lo1/lwa1, Be zoa < proto-Kam-Sui *s-lwa(n)A1 'boat'

"[劉]賈築吳市西城, 名曰「定錯」城。"

"[Líu] Jiă (the king of Jīng 荆) built the western wall, it was called dìngcuò ['settle(d)' & 'grindstone'] wall."

定 dìng < dengH < *adeng-s

← Siamese diaaŋA1, Daiya tʂhəŋ2, Sipsongpanna tseŋ2, Malay (Austronesian) dindiŋ2, Tagalog diŋdiŋ2 wall

錯 cuò < tshak < *atshak

? ← Siamese tokD1s 'to set→sunset→west' (tawan-tok 'sun-set' = 'west'); Longzhou tuk7, Bo'ai tɔk7, Daiya tok7, Sipsongpanna tok7 < proto-Tai *tokD1s ǀ Sui tok7, Mak tok7, Maonan tɔk < proto-Kam-Sui *tɔkD1, Malay (Austronesian) suntuk running out of time

Substrate in modern Chinese languages Besides a limited number of lexical items left in Chinese historical texts, remnants of language(s) spoken by the ancient Yue can be found in non-Han substrata in Southern Chinese dialects, e.g.: Wu, Min, Hakka, Yue, etc. Robert Bauer (1987) identifies twenty seven lexical items in Yue, Hakka and Min varieties, which share Kra–Dai roots.Bauer, Robert S. (1987). 'Kadai loanwords in southern Chinese dialects', Transactions of the International Conference of Orientalists in Japan 32: 95–111. The following are some examples cited from Bauer (1987):

to beat, whip: Yue-Guangzhou faak7a ← Wuming Zhuang fa:k8, Siamese faatD2L, Longzhou faat, Po-ai faat. to beat, pound: Yue-Guangzhou tap8 ← Siamese thup4/top2, Longzhou tupD1, Po-ai tup3/tɔpD1, Mak/Dong tapD2, Tai Nuea top5, Sui-Lingam tjăpD2, Sui-Jungchiang tjăpD2, Sui-Pyo tjăpD2, T'en tjapD2, White Tai tup4, Red Tai tup3, Shan thup5, Lao Nong Khai thip3, Lue Moeng Yawng tup5, Leiping-Zhuang thop5/top4, Western Nung tup4, Yay tup5, Saek thap6, Tai Lo thup3, Tai Maw thup3, Tai No top5, Wuming Zhuang tup8, Li-Jiamao tap8. to bite: Yue-Guangzhou khap8 ← Siamese khop2, Longzhou khoop5, Po-ai hap3, Ahom khup, Shan khop4, Lü khop, White Tai khop2, Nung khôp, Hsi-lin hapD2S, Wuming-Zhuang hap8, T'ien-pao hap, Black Tai khop2, Red Tai khop3, Lao Nong Khai khop1, Western Nung khap6, etc. to burn: Yue-Guangzhou naat7a, Hakka nat8 ← Wuming Zhuang na:t8, Po-ai naatD1L "hot". child: Min-Chaozhou noŋ1 kiā3 "child", Min-Suixi nuŋ3 kia3, Mandarin-Chengdu nɑŋ1 pɑ1 kər1 "youngest sibling", Min-Fuzhou nauŋ6 "young, immature" ← Siamese nɔɔŋ4, Tai Lo lɔŋ3, Tai Maw nɔŋ3, Tai No nɔŋ3 "younger sibling", Wuming Zhuang tak8 nu:ŋ4, Longzhou no:ŋ4 ba:u5, Buyi nuaŋ4, Dai-Xishuangbanna nɔŋ4 tsa:i2, Dai-Dehong lɔŋ4 tsa:i2, etc.