The writing system -- the transparency of orthography in alphabet-based systems and differences between logographic and phonetic-based systems -- can affect the efficiency of inferential word learning when words are introduced visually. It can also shape how people self-evaluate their learning success (we refer to such type of self-evaluation as metacognitive monitoring of word learning). By contrast, differences in metacognition and learning performance do not emerge when words are presented auditorily. To measure metacognition, we assessed retrospective confidence by asking participants to rate their certainty about the correctness of their responses. As this direct question raises a person's conscious awareness of how well they have learned a particular lexical unit, it allowed us to measure those aspects of metacognition that are modulated by consciousness. Such consciousness comes into play when a word is associated with an object. Differences in conscious awareness of the word learning success when words are represented visually make differential demands on word learning across languages and modalities. The observed differences between populations using different writing systems and between perceptual modalities may potentially modulate the effectiveness of vocabulary acquisition activities during foreign language learning.