Abstract : The interest in synthetic worlds for both language education (Cooke-Plagwitz, 2008; Molka-Danielson & Deutschmann, 2009) and architectural design (Gu. et al., 2009; Garner et al, 2011), coupled with the need of architects to develop adequate foreign language (L2) skills facilitating mobility and employability, led to the design of "Building Fragile Spaces." This hybrid Content and Language Integrated Learning (CLIL) course was held in Spring 2011. It included distance French and English L2 activities, conducted in the synthetic world Second Life, which incorporated both architectural and linguistic objectives. Our study of the "Building Fragile Spaces" course sheds light on how communication in the synthetic world is organised for pedagogical purposes. We focus on the usage and interaction between the text chat and audio modalities. Our analysis employs data provided from i) multimodal transcriptions of group reflective sessions, according to a predefined methodology (Mulce, 2011) which builds upon previous research (Ciekanski & Chanier, 2008), ii) post-course questionnaires and iii) interviews. We show how the text chat and audio modalities helped structure and support the L2 interactions. In particular, we describe the use of the text chat modality by tutors for linguistic correction and the incorporation of these corrections in the students' discourse.