<p><strong>Mandarin-as-a-foreign-language (MFL) courses are popular in English-medium international schools in China where international students are often bilingual or multilingual. These students may choose to communicate in more than one language. This research investigates teachers’ and students’ perceptions of language choices while teaching and learning MFL at an English-medium instruction (EMI) international school with an International Baccalaureate (IB) curriculum in Shanghai, China.</strong></p><p>This study combines García’s (2009) notion of translanguaging in dynamic bilingualism with Lave and Wenger’s (1991) theoretical framework of Communities of Practice (CoP) to explore the use of a common language (mainly English) in MFL learning. Both translanguaging and CoP were used to analyse how the participants engaged in the joint enterprises of teaching and learning Mandarin by utilising a common language from their linguistic repertoire. This study provides an understanding of how teachers and students negotiated their linguistic resources within their various CoPs, and how their mutual engagement and identities were reshaped by the practice of using a shared language.</p><p>This is a qualitative single case study. Data were collected through notes and memos, virtual classroom observations, semi-structured interviews, stimulated-recall interviews and focus group interviews. These data were complemented by artefacts from the school including class teaching notes, teaching plans and school policy documents. Two teacher participants were purposively selected and interviewed twice, and 32 secondary school student participants participated in focus group interviews. Data were transcribed, coded and analysed across the subcases to identify themes.</p><p>There are two main findings from this study. The first is that both teachers and the students chose to use a common language to mediate the students’ understanding and facilitate their foreign language learning. This contrasts with prior studies of how students’ first language and second languages work together. This study also reveals the students’ language choices as they were learning of IB concepts in the academic curriculum. IB learners are expected to develop asinternational-minded citizens and teachers are expected to strategically promote multiculturalism and multilingualism. This included a form of translanguaging that appeared to be unique to these MFL CoPs.</p><p>Purposeful, strategic and flexible translanguaging was achieved by the teachers’ and students’ practice of using a common language, English, as a bridge to the target language, Mandarin. The findings indicate that the teachers planned translanguaging into their lessons and also engaged in spontaneous translanguaging during class. This intentional use of translanguaging seemed to actively engage the students in learning the new language. The translanguaging employed by teachers encouraged students to communicate in their common language, and thus offered rich opportunities for language learning. The findings suggest that the student participants prioritised making sense of what their learning over using the target language, and the common language was a mediating force that scaffolded students' comprehension and influenced their motivation to participate in lessons. The students felt that their language choices for communicating in MFL classes were respected and they were acknowledged as multilingual members of this community.</p><p>This study provides insights for language teachers and educators about the positive role of including a common language in translanguaging spaces at IB international schools. This has implications for IB international schools which may adhere to a monolingual language policy in the teaching of foreign languages. It may also encourage language teachers who strive for active engagement by illustrating how creating a translanguaging space allows teachers to balance the school’s language policy and their pedagogical practices. The role of translanguaging may function differently in different contexts, but it honours students’ and teachers’ agency in their teaching and learning spaces. Translanguaging highlights the benefits of using shared elements of the participants’ linguistic repertoires, not only for developing MFL proficiency, but also for promoting class participation from beginning language learners.</p>