Teachers beware: L3 cognates may be difficult to learn. Spelling errors and the multilingual mental lexicon

Cognate words are supposedly easy to learn because they share orthographic and semantic similarities across languages. Still, cross-linguistic influence (CLI) from previous languages may work to the learner's disadvantage by triggering errors. We examine spelling errors in 120 Italian words made by L1-Polish learners of L3-Italian with L2-English (N = 93, Mage = 21.82, SD = 3.31). In our previous study (Authors, 2025), we tested the productive knowledge of words translated from learners' L2-English to L3-Italian (40 noncognates, 40 L2-L3 cognates, and 40 L1-L2-L3 cognates). Here, we focus on those learner outputs that were considered incorrect in the previous study, but whose spelling resembled the expected Italian keywords (N = 977). We classified these incorrect answers as (a) containing a CLI-related error, (b) exhibiting CLI from L1-Polish, L2-English, or both, (c) comprising an error in the stem, in the suffix, or both. Our results showed that the L1-L2-L3 cognates rendered significantly more CLI-related errors than the L2-L3 cognates and non-cognates. Importantly, in the L1-L2-L3 cognates, participants' L2-English was a more frequent source of CLI errors than their L1-Polish. We also observed that CLI-related errors were significantly more likely to occur in word stems than in suffixes, and their frequency in learner outputs decreased with the growing proficiency in L3-Italian. We discuss the results in relation to the Parasitic Model of the multilingual mental lexicon (Ecke, 2015). Finally, we propose pedagogical implications for language classrooms stemming from the types of spelling errors made in L2-L3 and L1-L2-L3 cognates.