This study is a replication and extension of Morgan-Short et al.'s (2018) investigation into the role of attention in input processing by L1-Polish learners of L2-Spanish, with proficiency and language of assessment explored as two key methodological factors. Our aims were twofold: to investigate learners' comprehension in different conditions with their L2 proficiency controlled for, and to examine this process when learners were tested using different languages. Data from three trials (N = 136) were analyzed: Trial-English, Trial-Polish, and Trial-Spanish, where comprehension was tested in English, Polish, or Spanish, respectively. Results showed that both L2 proficiency and language of assessment significantly affected learners' performance, with their scores being lower in the -n morpheme condition but only when comprehension was tested in English or Spanish. We discuss these findings both theoretically and methodologically, making recommendations on designing future replication studies and improving the generalizability of L2 findings across multiple research sites.