Little research explored how frequently and for what functions translanguaging occurs during second language (L2) writing processes. To fill this research gap, the study analysed translanguaging occurrences in 53 undergraduates' L2 writing processes. Translanguaging data were collected through think-aloud protocols, computer screen recordings, stimulated recall, and written drafts. Data analyses yielded four main findings: (1) on average, learners of varied L2 proficiency levels translanguaged frequently during their L2 writing processes; (2) reasoning was the least frequently performed translanguaging function, while repetition was the most frequently performed translanguaging function; (3) the lower-level L2 students performed translanguaging significantly more often than did their higher-level counterparts; (4) the higher-level L2 students translanguaged for monitoring significantly less often than did their lower-level counterparts. This study can contribute to the literature on translanguaging by exploring cognitively mediational roles of translanguaging and examining potential influences of L2 proficiency on the frequencies and functions of translanguaging.