Code use, including codeswitching and/or style-shifting, is an important but undertaught aspect of L2 sociolinguistic competence, and an important aspect of L2 learners' translanguaging repertoires. This study examines code use in Arabic--a diglossic language with distinct social uses for the prestige variety (Modern Standard Arabic, MSA) and Colloquial Arabic (CA). The study involved 10 participants who were third-year, L2 learners of Arabic in a multidialectal program, and focused on the questions: (1) What types of metasociolinguistic awareness are evident among advanced learners of Arabic who have had multidialectal training? (2) To what extent is this awareness reflected in their productions? Data collection included a language learning history survey, spoken and written productions in Arabic, and an English interview. Findings show that participants had a complex awareness of MSA-CA use that could be further expanded through instruction, suggesting that the trajectory of sociolinguistic competence development is complex, nonlinear, and influenced by instructional, social, and idiolectal factors. This study has important scholarly and pedagogical implications, and is linked to the rapidly growing body of scholarship on translanguaging practices and pedagogies.