The present study, situated within the field of Second Language Acquisition, allows us to broaden our understanding of the linguistic impacts naturalistic environments have on second language learners. The aim of this study is to investigate the development of lexical conventional sequences (CS) used by second language learners throughout an academic year spent in the country of their target language. The linguistic feature that we are focusing on (specific sequences of words used together, retrieved and stored as chunks) has been described by recent studies as an indicator of very advanced and native speakers’ speech. Lexical CS, more specifically, are considered to be the most difficult for L2 learners to acquire. Generally, while recent research shows the importance of naturalistic environments in language acquisition, results tend to vary significantly from one learner to another. While some show notable improvements after a year in a naturalistic context, others do not improve at all. Investigating, then, the impacts such environments have on a linguistic feature typical of native speech allows us to evaluate the influence native speakers’ speech has on L2 learners. The materials used in this investigation are interviews carried out by LANGSNAP. We focus on 15 L1 English speakers, who have studied French at a UK university, and study their longitudinal data – recorded before, during, and after 9 months spent in France. In order to compare their data with native speakers’ speech, the interviews (held in the same context) of 7 L1 French students were selected as well. The number of lexical CS and the number of words were counted in each interview, and the ratio of CS per 1000 words was calculated. We were then able to notice the changes occurring throughout the process. It appeared that the difference between the students who felt included in the French speaking community and those who mainly stayed with English speakers was striking. The former had adopted a lexical CS use similar to the native speakers’, while the latter did not evolve regarding this feature. The learners’ testimonies on how well they blended in with their L2 speech community indeed enabled us to analyse the linguistic feature in parallel with their personal investment, which allowed us to come to this conclusion. Accordingly, an English L1 speaker can adopt a native French speakers’ use of lexical conventional sequences, however it appears to be dependent on whether the learner has genuine relationships with French speakers and feels included in the speech community. We suggest that future studies investigate the factors relevant in helping to maintain these acquired features, after such experiences, when the learner is no longer in a naturalistic environment.