While extensive research has illustrated the importance of translingual practices in multilingual education, there is limited understanding of how language teachers develop the knowledge to teach L1 and L2 simultaneously. This paper seeks to conceptualise teacher professional knowledge through narrative inquiry, focusing on Chinese language teachers in Hong Kong's mainstream schools who teach both native Chinese and non-Chinese-speaking (NCS) students. This study explores how L1 Chinese teachers develop their professional competencies to aid L2 Chinese learning among NCS students in multilingual settings requiring multiple teaching roles. Drawing on in-depth narrative interviews with ten Chinese language teachers who instruct Chinese as both an L1 and an L2, this study identifies, systematises, and theorises the professional repertoire of translingual practice. The data reveal a multifaceted professional repertoire comprising three trans-dimensional areas of expertise: transpedagogical knowledge, translingual dispositions, and transprofessional capacities. This paper emphasises the need for a 'translingual teacher cognition' perspective, grounded in translanguaging scholarship, to provide a deeper insight into how teachers build their professional knowledge in schools serving diverse student groups.
