“…Learning a second language (L2) can be difficult for a variety of reasons. Pedagogical context (Tagarelli et al, 2016), cognitive processing differences across learners (Ellis, 1996;Yalçın and Spada, 2016), L2 structural complexity (Pallotti, 2015;Yalçın and Spada, 2016;Housen et al, 2019), or similarity between the target L2 and the learner's first language (L1) can all conspire to affect the speed and success of L2 acquisition (Hyltenstam, 1977;Lowie and Verspoor, 2004;Foucart and Frenck-Mestre, 2011;Málek, 2013;Schepens et al, 2013;Türker, 2016;Carrasco-Ortíz et al, 2017). Similarity, in particular, is a difficult variable to examine, because it is so hard to pin down.…”