The present study aimed to position foreign language curiosity within the nomological network of key emotional and behavioural variables in foreign language (FL) learning. Drawing on an international sample of 345 FL learners, we examined the relationships among curiosity and enjoyment, anxiety, and boredom, as well as their links to willingness to communicate (WTC), engagement, and academic achievement using a structural equation model. Results indicated that curiosity was strongly and positively associated with enjoyment, and negatively associated with anxiety and boredom, supporting its role as a positively valenced construct within the FL emotional system. Furthermore, curiosity emerged as a significant positive predictor of both WTC and engagement, alongside enjoyment, while anxiety negatively predicted WTC. In contrast, boredom did not significantly predict WTC, suggesting differential pathways between deactivating emotions and communicative behaviour. Both WTC and engagement were found to positively predict academic achievement. These findings highlight the central role of curiosity as an active motivational and emotional driver in language learning and underscore the need for future research to further embed curiosity in explanatory models of FL learning.