Abstract: The territory of the Belarusian-Polish borderland during the first half of the 20th century was the arena of a conflict between two important political and cultural centers — the USSR and Poland, that fought for supremacy in Eastern Europe and dominance on the territory of Belarus. Within the framework of this conflict, interethnic relations developed between the Poles and the Belarusians, in particular, on the territory of Bialystok, Brest, Grodno and Western Polesia. The subject of this study is such aspects of the relations between the two peoples as identification by language. One of the most important manifestations of this confrontation was the status of the Belarusian language, as well as its codification. In the period under study, there were regional variants of the Belarusian language, any of which could potentially be taken as the basis for the creation of the grammar of the literary language, which is why the normativization of this language became one of the collision fields of the two historical centers towards which the region's population gravitated — Moscow and Warsaw. The article's main research method is the comparative method, which has allowed to uncover the particularities of the language policies of the Soviet power and the Polish administration, including the influence of their underground agencies during the years of the war on the ethnic conflict. The novelty of this article lies in its attempt to move away from the common in works of Polish, Belarusian and Soviet scholars presentation of the total opposition (based on undeniable historical facts and the logic of state- and nation- building in the 20th century) of the two ethnic communities of the region: the Poles and the Belarusians, in favor of illuminating the particular regional "local" identity, which never ceased to form despite the objective existence of the Belarusian-Polish conflict.