This themed section explores linguistic disadvantage as a key form of structural-institutional disadvantage in welfare societies, focusing on how language policies, practices, and ideologies shape migrant background service users’ access to services, rights, and social protection. The novel contribution by the team of authors with a background in social policy, social work, sociology, and ethnology is to fill existing conceptual and empirical gaps by advancing a relational view on multilingualism and linguistic diversity and highlighting the critical importance of language in institutional policies and practices and in the everyday encounters and relationships between service users, the welfare state and its representatives. The articles represent a rich variety of national and cross-national research, drawing on empirical case studies from Finland, Sweden, Belgium, and Canada. By situating language practices within broader social, political, and cultural struggles, the section calls for social policies and practices that challenge monolingual ideals and promote plurilingual ways of knowing.