The article deals with the description of language interference as the main process in creating the regional identity of the Russian language in Donbass. The relevance of the work is determined by the fact that it is the first attempt to identify the role and forms of language interference in the formation of a regiolect, moreover, the object of research of the processes of language systems interaction is the Donetsk diffuse regiolect, which arose on the South Russian language base as a result of interference of closely related languages and regiolects. The stated subject involves the identification of types, zones, models and participants of interference interaction. The purpose of the article is to determine the sources and results of language interference that occurred during the formation of the Donetsk diffuse regiolect. The author uses general scientific and linguistic methods and techniques for analyzing regionalisms, in particular, comparative, descriptive methods, methods of collecting and processing sociolinguistic data, specialized methods for determining regionalisms. The use of basic methods of analysis and synthesis, as well as the observation method when considering Donetsk language phenomena, allowed the author to determine the Russian basis of the Donetsk regiolect, its diffuse nature, to justify the implementation in regional modifying the “interference absorption” model of external (different language and different regiolect) and internal (idiom) language phenomena, to establish the language zones of interference interaction, the main language systems that participated in the formation of the Donetsk regiolect, and the degree of their participation in this process. The obtained theoretical conclusions can be used in the study of the regiolects of the territories of late settlement, formed on the basis of closely related languages and regiolects, for example, Russian and Ukrainian, Russian and Belorussian, etc.