ABSTRACT By following Johann Gottfried Herder's cultural nationalism, the paper illustrates the centrality of languages in the formation of modern nation states. Herder further enables us to comprehend the significance of a common cultural core for national unity; the negative role of uniformity that leads to exclusionary policies; and the development of dissension into armed conflicts among ethnicities and nations. Thus, Herder reveals that linguistic nationalism takes the dangerously ethnic turn when its civic elements are not properly utilised. Through Herder's method, I demonstrate the cause of conflict between language and cultural rights and other human rights. For this, I examine why the peoples of Sri Lanka and undivided Pakistan defined themselves primarily in ethnic terms during decolonisation and in religio-linguistic terms after independence. By comparing the 1930s’ Sri Lankan vernacular (Swabasha) movement with the language movement (Bhasha Andolon) of 1952 in the then East Pakistan (now Bangladesh), I delineate the nature of challenges that marginalised peoples face regarding their cultural rights in decolonised societies. Since the societies require clear directions for nurturing ethnic cooperation, I suggest that the strategic aspects of Herder's idealism can pave the way for this.