Interview-based research in multilingual situations can present researchers with specific ethical challenges relating to language-based power play, data handling and presentation. Studies indicate favouring the L1 (first language) as an interviewing language may produce better quality data, but external pressures can favour English as the dominant research language. This article examines researcher perceptions and experiences of the ethical consequences of language choice and the practical issues involved. Interviews were conducted with five European researchers working on an interview-based project with experiences of diverse interviewing scenarios. The four moral principles of respect for autonomy, justice, beneficence and non-maleficence were used as a framework for analysis. The analysis revealed a nuanced picture of ethical issues in both L1- and English-oriented scenarios. This included potential misrepresentation and deculturalisation of the data in the former, and language-based power asymmetries in the latter. The findings highlight the importance of documenting ethics-related methodological details of language use, and advocates publication practices favouring the inclusion and foregrounding of L1 data.