To investigate the differences in communicative activities by the same interlocutors in Japanese (their L1) and in English (their L2), an 8-h multimodal corpus of multiparty conversations was collected. Three subjects participated in each conversational group, and they had conversations on free-flowing and goal-oriented topics in Japanese and in English. Their utterances, eye gazes, and gestures were recorded with microphones, eye trackers, and video cameras. The utterances and eye gazes were manually annotated. Their utterances were transcribed, and the transcriptions of each participant were aligned with those of the others along the time axis. Quantitative analyses were made to compare the communicative activities caused by the differences in conversational languages, the conversation types, and the levels of language expertise in L2. The results reveal different utterance characteristics and gaze patterns that reflect the differences in difficulty felt by the participants in each conversational condition. Both total and average durations of utterances were shorter in their L2 than in their L1 conversations. Differences in eye gazes were mainly found in those toward the information senders: Speakers were gazed at more in their second-language than in their native-language conversations. Our findings on the characteristics of conversations in the second language suggest possible directions for future research in psychology, cognitive science, and human-computer interaction technologies.