This study addresses the question of how Europe’s liberal democracies should respond to post-immigration linguistic diversity – that is, the array of languages spoken by non-dominant linguistic groups of immigrant origin. Drawing on broader principles of justice, I argue that liberal democratic states owe a threefold set of obligations to the members of such groups. First, as a correlative of widely recognised fundamental freedoms, such states should tolerate the existence of post-immigration linguistic diversity, requiring them to refrain from interfering with individual (private) language use. Second, such states should also accommodate individuals’ linguistic needs – for instance by providing translation and interpretation – in order to ensure that language is not a barrier to the effective enjoyment of their human rights and to facilitate their access to essential services on a non-discriminatory basis. Third, liberal democracies in Europe should also promote immigrant-origin languages in order to ensure that non-dominant linguistic groups are treated evenhandedly with respect to the maintenance of their distinct linguistic identities. I then show that these three sets of obligations are largely captured – albeit in fragmentary form – in the normative architecture of international law, in particular in international human rights law and in the international instruments protecting migrants and minorities. Finally, I assess the extent to which these obligations are also reflected in the current practice of Germany and the UK, drawing together analysis of domestic law and policy and empirical insights from interviews with community representatives and public officials. This analysis reveals a range of relevant practices, including ‘heritage language’ teaching for immigrant-origin groups in state schools, the provision of translation and interpretation in public service delivery, and the symbolic inclusion of immigrant-origin languages on public street signage. These practices demonstrate that my account of linguistic justice for immigrant-origin groups in Europe can – and should – be made a reality.