The issue of polonisation and the status of the Polish language has been the subject of intense interest in Lithuania to this day, not only in a cultural and historical context, but also in a political context, since Poles constitute the largest national minority there. This article is an attempt to describe the role of the linguistic aspect in the national transformations in Lithuania during the crucial period, i.e. the formation of modern national identities at the turn of the 19th century and their emancipation in the form of the politics of national states of the interwar period. The analysis includes a number of statistics on the presence of Lithuanian and Polish language in public space and their place in the context of a political, social and economic situation of Lithuanian territories. The creation of national states and the formation of linguistic and national processes from the top down by state administration were commonplace on both sides of the Lithuanian-Polish border. In Polish-Lithuanian relations it was the language that became the main hostage of the conflict and a kind of litmus paper for defining national identity, thus marginalising other aspects.