Helsinki and Barcelona are particularly interesting cases for the study of the challenges associated with present-day multilingualism, due to their combining a well-entrenched endogenous patrimony of linguistic diversity, together with the politics this patrimony has entailed, with new layers of exogenous linguistic differentiation introduced by recent waves of immigration. As a result, the linguistic cleavages of the past intermingle in intricate ways with the imprint of the new heterogeneity. The assessment of the politics of multilingualism in the two cities demonstrates, on the one hand, how the national is "transnationalized" due to the new cultural and communicative practices introduced by immigrant groups. On the other hand, the politics of multilingualism is a politics that nationalizes the transnational: although the "hybridization" that is often associated with the dynamics of immigration may well change the parameters of identity politics, it apparently does not entail the waning of all cultural identities in a cosmopolitan pastiche of sorts. The analysis presented leads to the normative conclusion that the recognition of linguistic identities plays a key role in linking the dynamics of complex diversity and citizenization. By just political standards, cities concerned with how to confront a diverse citizenry should open up to introduce varying combinations of a multilingual repertoire at the level of their institutions.