More than half of the world’s displaced population has moved to urban or peri-urban areas, and in Brussels, the superdiverse Belgian and European capital, the emergency care sector provides an important setting for analysing the multilingual challenges faced by health practitioners. To gain a better insight in the interactional dynamics of emergency department consultations with immigrant patients, this paper focuses on multilingual strategies that include ‘ad hoc’ communicative solutions used in the absence of professional interpreters (lingua franca use, non-verbal communication, medical translation software, language mediation through companions or hospital staff). Despite their efforts, the participants in our two case-studies lacked the linguistic and interpreting subtleties needed to perform complex linguistic-interactional tasks, and in this way, a form of ‘false fluency’ was created. Ad hoc multilingual solutions, significant as they are, require additional language support to avoid diagnostic insecurity. At the level of patient management, a ‘linguistic assessment’ of patients could potentially be integrated into the triage process, and clinicians should be trained on how to recognise and remediate communication problems under the specific conditions of the emergency department.