Though applied linguistics has observed a rise in language acquisition investigations within the complex dynamic systems theory (CDST) paradigm, the majority of research endeavors have been centered on the development of learners' first language (L1) or second language (L2). Limited research exists on multilinguals’ L3 acquisition/development, with even fewer studies considering the development of learners’ speaking skill in L2, and L3. The present study aimed to address these gaps by adopting a CDST approach to analyze the development of fluency, accuracy, and complexity in L2 (English) and L3 (French) speaking skills among five undergraduate Iranian EFL junior students of Translation Studies at Jahrom University over one academic year. The students were at an intermediate level in English language and their French language proficiency was at the beginner level. The participants’ speaking ability in both languages was closely examined and analyzed regarding their development of fluency, accuracy, and complexity within a quantitative design. Findings depicted that the aspects were developed in non-linear, chaotic, and emergent patterns in multilingual learners’ L2 and L3 speaking skill. Moreover, the findings indicated that these elements in multilingual learners' speaking were interconnected and influenced each other over a period of time. The discoveries have some significant implications for L2 and L3 language teaching, such as creating flexible learning and teaching environments, fostering emergent behavior in language classrooms, encouraging learners to have a self-organizing and autonomous role in language learning, having sensitivity to the diverse needs of learners, and fostering a collaborative learning environment.
