Inspired by recent epistemological and ontological debates aimed at unsettling and reshaping conceptions of language, this essay discusses how mainstream sociolinguistics offers notions meaningful for studying contexts of the South. Based on empirical studies of youth in two African cities, Yaoundé in Cameroon and Maputo in Mozambique, the essay engages with ‘fluid modernity’ and ‘enregisterment’ to unravel the role that fluid multilingual practices play in the social lives of urban youth. The empirically grounded theoretical discussion shows how recent epistemologies and ontologies offer inroads to more pluriversal knowledge production. The essay foregrounds: i) the role of language in the socio-political battles of control over resources, and ii) speakers’ reflexivity and metapragmatic awareness of register formations of fluid multilingual practices. Moreover, it shows how bundles of localized meanings construct belongings and counterhegemonic discourses, as well as demonstrating speakers’ differential valuations and perceptions of boundaries and transgressions across social space.