Ингуши
According to the linguist Johanna Nichols, who studied languages including Chechen and Ingush in her book "Ingush Grammar" says: "To my surprise, Ingush turned out to be the most complex language of my sample, besting even polysynthetic languages like Seneca, Lakhota, and Halkomelem. Ingush is not polysynthetic; its complexity is due to large inventories of elements (phonemes, cases, tenses, etc.), a high degree of inflectional synthesis in the verb, and classification of various types – declension and conjugation classes, agreement genders, overt inherent genders, split verbal lexicon, split alignment, etc. Perhaps this complexity explains why it has taken thirty years to produce this grammar, during most of which time the project has in fact been on or near the front burner ... Ingush and Chechen are distinct languages and not mutually intelligible, but because of widespread passive partial knowledge of standard lowlands Chechen by Ingush they function to some extent as a single speech community." "Ingush is the native language of the great majority of the approximately 300,000 Ingush people, most of whom live in or near the Republic of Ingushetia on the north slope of the Great Caucasus mountain range in the South Russia ... Ingush and Chechen are distinct languages and not mutually intelligible, but because of widespread passive bilingualism they form a single speech community."