As the preeminent mobile social media platform in Mainland China, WeChat's meteoric expansion has revolutionized the dynamics of interpersonal communication and the modalities of mutual interaction among individuals. Despite the escalating significance of mobile social media in the cross-cultural adaptation of international students, existing scholarly works have largely neglected the underlying relationship between psychological motivations, excessive WeChat use, academic performance, and sociocultural adaptation of these students. Anchored in uses and gratifications theory and cross-cultural adaptation paradigm, the primary objectives of this study are to devise a theoretical model and to scrutinize differential psychological motivations propelling international students' WeChat usage, its association with excessive WeChat use, and impacts on academic performance and sociocultural adjustment. The proposed model undergoes meticulous evaluation through data amassed online from 598 Chinese international students studying in Germany. Sequential analytical techniques, especially Confirmatory Factor Analysis and Structural Equation Modeling, were employed to elucidate the dynamic interplay among key variables. The final results validate the path effect suggesting that both hedonic and social motivations are positive predictors of excessive WeChat use. Moreover, excessive WeChat use is negatively correlated with academic performance and sociocultural adjustment. However, utilitarian motivation is not significantly related to excessive WeChat use. By demystifying the driving factors and consequences of excessive WeChat use, these findings not only accentuate the pivotal role of mobile social media in the cross-cultural adaptation of international students but also enrich the theoretical landscape and enhance the strategic approaches for educators and academic institutions.