The problem of interference is one of the most complex issues related to language interaction, so it is especially important to investigate its workings on the example of the language of Russian Germans in the Kirov region. The article realises the historical and linguocultural approaches to the study of the interrelationship between folk-colloquial speech and the traditional culture of Russian Germans, residing on the territory of the Kirov region. The authors present the results of an in-depth analysis of interference features in the Russian speech of German bilinguals under the influence of the German language and its dialects, namely, the phonetic, lexical and grammatical features that occur under the influence of interference with the German language. The Russian speech of German bilinguals is heterogeneous and varies from “virtually without an accent” to “unnatural” for Russian monolingual hearing. The interaction of the Russian and German languages in the speech of German bilinguals resulted in the increased invasion of the norms of one language system into the framework of another language. This leads to the so-called levelling of the interacting languages. In other words, we see the emergence of a third – intermediate system that does not coincide either with the German or Russian languages and performs in the bilingual consciousness an adaptive function to the environment language. This study contributes to German dialectology, enriching both the theory and typology of island dialects, which retain archaic features and the theory and practice of scientifically grounded language policy and language preservation.