This paper reports on research conducted within the frame of an international online cooperation between Germany and Israel (CoGI). Diverse, multilingual student groups co-construct multilingual websites on educational initiatives. The aim is to raise prospective teachers' language awareness (LA) and cultural awareness (CA) for cooperation in international contexts. 75 students and five instructors from four different campuses in Germany and Israel took part in the project in 2019. Individual and cooperative learning was combined with online and face-to-face as well as student conference learning. A mixed-method approach was used to investigate the effects of the 10-week cooperation with respect to the emergence of LA and CA as well as perceived language proficiency. The results show a significant increase in participants' perceived English language proficiency and CA. The qualitative analyses give evidence of co-constructive group cooperation which revealed LA and CA in the process of negotiating shared understanding. The study highlights the importance of international online cooperation in teacher education.