This cross-sectional study addresses for the first time the non/linear association between individual learner differences of social, proficiency-related, and socioaffective nature (length of residence [LoR], varietal proficiency, exposure, and socioaffect) and differential outcomes in L2 sociolinguistic repertoires against the backdrop of the Austro-Bavarian naturalistic context. Forty adult migrant L2 German learners participated in a virtual reality experiment involving interactions with dialect-speaking and standard German-speaking interlocutors. The goal was to explore differences in participants' interpersonal varietal behavior, that is, their addressee-relational variable use of standard German, Austro-Bavarian dialect, and mixture varieties. The results of Bayesian multinomial modeling indicated that LoR, dialect exposure, and proficiency, as well as reduced anxiety when speaking dialect, predicted differences in interpersonal varietal behavior. That said, a visual-quantitative analysis revealed critical thresholds concerning when, within these predictors, changes in sociolinguistic behavior manifested, indicating a rapid change in sociolinguistic development at the inter-individual level and ultimately facilitating initial insights as to how advanced one needs to be in order to engage in sociolinguistic variation in the Austro-Bavarian naturalistic context.