For agentive and influential involvement in online communities, language learners and teachers need to develop critical digital literacy (CDL), conceptualized by Darvin (2017) as an awareness of "how meanings are represented in ways that maintain and reproduce relations of power" (p. 5) and thus privilege some and marginalize others online. Virtual exchange (VE) provides an ideal socio-cultural and socio-semiotic context for fostering CDL (Hauck, 2019) as it is an educational intervention that is--by default--digitally mediated. In this contribution, we examine the employment of semiotic practices for multimodal representation and how they "shape power relations with others" (Bezemer & Jewitt, 2009, p. 1), thereby drawing on a social semiotic approach (Bezemer & Kress, 2016) to CDL (Bilki et al., 2023). Our insights stem from a six-week VE between two higher education institutions in Turkey and the UK, which brought together 48 future English as a Foreign Language (EFL) teachers. The task-based exchanges yielded a rich dataset which allows us to illustrate how CDL is materially achieved through transformative processes observed in multicultural, multilingual, and multimodal interactions. Our findings speak to Kern's (2014, 2015) appeal for a relational pedagogy and highlight the need to promote CDL in EFL teaching and teacher education to foster critical reflection on meaning-making conventions while exercising agency to establish powerful online relations with others.