Generative AI is increasingly embedded in language learning contexts as a language-producing system that interacts with learners, models, amplifies, and in some contexts actively reshapes linguistic norms, while influencing language across educational and digital spaces. This poster examines the sociocultural consequences of generative AI when it functions in the role of a participant rather than solely as a mediating tool. Here, participation is understood as a functional and relational role in interaction, not as evidence of intention, consciousness, or autonomous agency. From a sociocultural perspective, AI participation reshapes communities of practice and speech communities by contributing to norm-setting, authority, and legitimacy. In some contexts, AI stabilizes dominant registers and tones; in others, it amplifies, introduces, or accelerates emerging norms, including slang, euphemism, and ideologically charged language. When AI produces language alongside learners, assumptions about effort, authenticity, and developmental trajectories are reconfigured. Learner identity, investment, motivation, and affect are shaped through altered experiences of belonging, safety, anxiety, and recognition as legitimate speakers. By foregrounding AI participation, this poster isolates how sociocultural effects emerge through norm circulation and co-construction, offering a conceptual entry point for examining how participation itself is being redefined in AI-mediated language learning contexts.