This case study sheds important light on ethnic multilingual speakers’ identity construction in their multilingual lived experiences. An ethnic multilingual speaker (pseudonym Altan) of Mongolian (L1), Mandarin (L2), English (L3) and Japanese (L4) was selected as a case study to present his self-conflict in the practice of moving between languages. This case study provides a long-term view of how an ethnic multilingual speaker’s ethnic (language) awareness was awoken when struggling between speaking different languages and how he tried to prioritise and ‘legitimize’ his ethnic identity in a Mandarin-dominated society. The participant was interviewed with twelve open-ended and semi-structured questions. Following the guidance of Interpretative Phenomenological Analysis (IPA), the transcript was translated and analysed line by line, with two rounds of exploratory notes. To better understand the multilingual lived experience of the participant, this study adopts monolingualism, translingualism and identity theories to interpret the participants’ language-related self-conflict. The study not only highlights the subtractive side of translanguaging but also implies that some multilinguals may not find comfortable spaces to maintain and develop their ethnic identity in multilingual contexts. The salient ‘self-conflict’ caused by the ‘visible’ and ‘invisible’ translanguaging also makes a unique contribution to the field of ethnic multilingualism.