Ruanruan (), also called Rouran (), is an unclassified extinct language of Mongolia and northern China, spoken in the Rouran Khaganate from the 4th to the 6th centuries AD, considered a likely early precursor to Mongolic.
Peter A. Boodberg claimed in 1935 that the Ruanruan language was Mongolic by analysing Chinese transcriptions of Ruan-ruan names. Atwood (2013) notes that Rourans calqued the Sogdian word pūr "son" into their language as *k’obun (Chinese transliteration: 去汾 MC *kʰɨʌH-bɨun > Mandarin qùfén); which, according to Atwood, is cognate with Middle Mongol kö'ün "son". Alexander Vovin noted that Old Turkic had borrowed some words from an unknown non-Altaic language that might have been Ruan-ruan, arguing that if so, the language would be non-Altaic, unrelated to its neighbours and possibly a language isolate, though evidence was scant. In 2019, with the emergence of new evidence through the analysis of the Brāhmī Bugut and Khüis Tolgoi, Vovin changed his view, suggesting Ruan-ruan was, in fact, a Mongolic language, close but not identical to Middle Mongolian. Pamela Kyle Crossley (2019) wrote that the Rouran language itself has remained a puzzle, and leading linguists consider it a possible isolate.
Phonology
Features of Ruan-ruan included: no mid vowels presence of initial l- final consonantal cluster -nd unusual for any "Altaic" languages
Morphology
Ruan-ruan had the feminine gender suffix -tu-.
Lexicon
Ruan-ruan vocabulary included: küskü – 'rat' ud – 'ox' luu – 'dragon' < Middle Chinese luŋ – 'dragon' yund – 'horse' < - 'horse' laγzïn – 'pig' qaγan – 'emperor' qan – 'khan' qaγatun – 'empress' qatun – 'khan's wife' aq – 'dung' and – 'oath' < 'oath' beg – 'elder' bitig – 'inscription' bod – 'people' drö – 'law' küǰü – 'strength' < 'strength, power' ordu – 'camp' tal- – 'to plunder' törö – 'to be born' türǖg – 'Turk'