It is often observed that the globalization of social media has opened up new opportunities for informal intercultural communication and foreign language learning. This study aims to go beyond this general observation through a case study that explores how discourse analysis tools might be used to uncover evidence of language and intercultural learning in comments on YouTube videos involving Chinese-English translanguaging. Analysis of exchange structure--interactional acts involving information exchange and stance marking--suggests that translanguaging triggers interactionally-rich comments that are oriented towards information exchange and negotiation for meaning on topics of language and culture. It is argued that the methodologies used have good potential for use in studies that aim to investigate learning in online settings, both at the environmental level, in macroanalysis of large data sets, and at the individual/situational level, in microanalysis of shorter interactional sequences.