Human language and cognition do not develop independently of each other but are intricately intertwined in various ways. This contribution presents the interplay between linguistic and cognitive abilities of learners at the individual level and relates them to the level of external contextual factors in social and educational environments. In empirical research, it is important to differentiate between so-called proximal and distal external factors: A causal effect on the individual learner can be primarily assumed through the direct stimulation of proximal factors, i.e., in personal interaction (Proximity of Stimulation approach, Kersten 2020, 2023). Therefore, external factors should be differentiated and special attention should be given to the proximal factors as direct influencing factors in empirical studies. This contribution begins with some terminological clarifications. In the following section, the connections between individual linguistic and cognitive development are discussed using selected variables in both directions (internal perspective). Initially, findings regarding the influence of multilingualism on cognitive abilities are examined, followed by the influence of cognitive abilities on L2 acquisition in the reverse direction. Finally, the contribution focuses on external contextual factors. Findings on family contextual factors such as linguistic and social background are presented. Lastly, educational contextual factors are explored, particularly discussing whether and how instructional factors can contribute to creating conducive conditions for mutual development in both domains, cognition and language, and potentially compensating for disadvantaged learner groups (cf. Kersten 2019). [This is the translated version of originally published title "Der Zusammenhang von kognitiven Fähigkeiten und Mehrsprachigkeit im frühen L2-Erwerb: Individuelle und externe Variablen," which was published in: "Language Education and Acquisition Research: Focusing Early Language Learning," edited by H. Böttger et al., Klinkhardt, 2020, pp. 82-116.]