Feedback within the context of post-observation conferences (POCs) is critical for English language teachers' professional development. To date, however, surprisingly there has not yet been any study on language choices for feedback communication in POCs, considering around 80% of English language teachers worldwide are nonnative-English speakers (NNESs) (Moussu, 2018). This study adopts the research paradigm of social constructivism, with a qualitative design to explore language choices (Chinese as L1 and English as L2) by one Chinese mentor and four Chinese mentees in POCs, in a near-peer mentoring project in a UK-based MA TESOL program. Data collected include two POCs, a mentor interview, and four mentee questionnaire answers. The data were analysed in depth by data reduction and inductive content analysis. It was found that both emotional and practical reasons resulted in the language decisions by the mentor and the mentees in the POCs. Albeit with small sample size, this study shows the intricacy of language use by NNESs in POCs in preservice teacher education programs and provides insights into how both mentor and mentees can be empowered as active agents capable of making judicious use of L1 and L2 for effective feedback communication in POCs.