This is seen through the lens of the collapse of Nation-State borders that crumble in the face of migration and the intense flow of languages that comes with it. It brings together international research that problematizes, theorizes, re-positions and re-conceptualizes myriad structural, systemic, ideological, political and pedagogical issues that intersect with the possibilities and impossibilities of the development of language teachers' agency. The volume examines the needs of linguistically diverse student populations and considers the socio-cultural and socio-political barriers that interfere with the exercise of teacher agency for social justice in language classrooms. It offers a theoretical and empirical overview of how language teacher education has addressed multilingualism and transculturalism in critical approaches in many complex countries in their diversity and/or postcolonial history, including Brazil, Qazaqstan, Scotland, and Thailand.