It is widely accepted that learners' previous linguistic knowledge and language learning experience play an important role in the process of acquisition and use of an additional foreign language. One of the factors purported to facilitate or constrain the exploitation of previous background knowledge in the process of acquisition of an L3 is psychotypology, learners' perception of the typological proximity between the language systems in their repertoire. It is claimed that the most prominent features of similarity between languages are similarities at the lexical level, or the existence of cognate forms between languages regardless of whether they owe their existence to genealogy or contact (Hall et al. 2009; Ringbom 2007). However, similarity can be determined only in relative terms (depending on a particular language constellation) and its position depends on both typological similarity and language contact. The present study aims to examine psychotypological beliefs of 189 multilingual high school learners of English as L3 living in officially bilingual Croatian-Italian communities in Istria County in Croatia. More precisely, we examine what the learners with background knowledge of Croatian and Italian base their judgments on in the assessment of similarity between English and other languages in their repertoire, and how they form judgments about the ease or difficulty of learning English depending on which of the two background languages is their mother tongue. The data were collected using a multiple-choice psychotypology questionnaire based on Hall et al. (2009), which was slightly modified and supplemented with open-ended questions in which the learners were asked to explain in more detail the reasons behind the choices made in the questionnaire. The results are analyzed taking into consideration the language constellation of three genealogically unrelated languages, sociolinguistic and socioeducational context and both theoretical and practical implications are discussed.