This thesis presents a linguistic ethnographic case study on a large Chinese complementary school (CCS) in Birmingham, England. Guided by Bakhtin’s theory of heteroglossia, the study investigates multilingual practices of adult participants in and around the school, focusing on the changing constructions of language ideology, Chinese teachers’ professional identity and the ethnic identification of Chineseness. It documents the impact of globalisation on the shifting relations among Chinese varieties and English in the Chinese diaspora. The 10-month fieldwork for the study was conducted in 2013/14 academic year, with observations and interviews as dominant methods for data collection. Main findings are: (1) an ideological ecology including ‘separate bilingualism’, ‘translanguaging’, ‘a hegemony of Putonghua’, and ‘a preferred school-wide monolingualism’ is dynamically constructed in the school. ‘Language as pride’ and ‘Language as profit’ are simultaneously in play leading to the dynamic ecology; (2) Chinese teachers’ professional identities are shaped by the changing structure of Chinese diaspora, the shifting power balance among different Chinese varieties and English, and teachers’ own biographical trajectories of settlement into English society; (3) practices in CCS context reflect an evolving ethnic identification of diasporic Chineseness which ‘de-freezes’ from a cultural heritage affiliated purely with the past and the national homeland.