We argue that quantitative analysis of community-based speech data furnishes an indispensable adjunct to theoretical and experimental studies targeting the acquisition of relativization. Drawing on a comparative sociolinguistic approach, we make use of three corpora of natural speech to investigate second-language (L2) speakers’ acquisition of restrictive relative clauses in English. These corpora comprise: (i) spontaneous L2 speech; (ii) a local baseline variety of the target language (TL); and (iii) L2 speakers’ first language (L1), French. These complementary datasets enable us to explore the extent to which L2 speakers reproduce the discursive frequency of relative markers, as well as their fine-grained linguistic conditioning, in the local TL baseline variety. Comparisons with French facilitate exploration of possible L1 transfer effects on L2 speakers’ production of English restrictive relative clauses. Results indicate that evidence of L1 transfer effects on L2 speakers’ restrictive relative clauses is tenuous. A pivotal finding is that L2 speakers, in the aggregate, closely approximate TL constraints on relative marker selection, although they use the subject relativizer who significantly less often than their TL counterparts. We implicate affiliation with, and integration into, the local TL community as key factors facilitating the propagation of TL vernacular norms to L2 speakers.