This paper examines diasporic language ecology based on a sociolinguistic study of a Chinese complementary school (CCS) in Birmingham, England. The study applies a historical perspective to investigate local multilingual practices in relation to language ideology and identity. The discussion in this paper draws on "heteroglossia" to investigate language stratification in the CCS. It documents the impact of global mobility and socio-economic changes on shifting power relations among two Chinese language varieties ("Putonghua" and "Cantonese") and English. Data for the discussion includes audio-recordings of interaction and interview as well as fieldnote vignettes. Findings show that (1) a stratified ideological ecology including 'separate bilingualism', 'translanguaging', 'a preferred school-wide monolingualism', and 'a standard language ideology' is dynamically constructed and negotiated in the school as a local heteroglossia; (2) At the intra-Chinese level, the Chinese language shift from Cantonese to Putonghua at global level is seeing its power in the local discourses of Putonghua becoming 'the new diasporic standard'. This standardisation towards Putonghua, on one hand, is claimed and celebrated in the school by some Putonghua-speaking members as 'practical' and 'useful' for better communication; on the other side, it is also contested -- sometimes silently -- in tension-filled local interactions by groups of Chinese people who lack the resource of Putonghua in their repertoires. This complex and tension-filled standardisation of diasporic Chinese language provides new local discourses of global mobility and the ongoing conversion from linguistic standardisation to social inequality.