Second language (L2) vocabulary learning is one of the most important aspects of second language acquisition (SLA). Its enormous importance, paired with the rapid development of mobile-assisted language learning (MALL), has led to increasing use of mobile-based dictionaries (MBDs) by English as a Foreign Language (EFL) learners at Chinese universities, especially for self-directed informal language learning. Although many studies have explored the role of dictionaries in Chinese learners’ L2 vocabulary learning, few have considered mobile-based dictionaries (MBDs). This study examined three types of MBDs: monolingual, bilingualised and bilingual. It aimed to investigate: (1) whether and how MBDs facilitate Chinese university EFL learners’ incidental vocabulary learning, (2) how learners use MBDs and (3) their attitudes toward MBDs.

Participants comprised 66 English majors and 59 non-English majors. This study used two questionnaires, pre- and post-tests as well as interviews to collect quantitative and qualitative data. The results of the self-report questionnaire show that Chinese EFL learners are selective when using MBDs for reading. They prefer to look up word definitions, especially first definitions and Chinese translations. The non-English majors use MBDs more often than the English majors, especially in searching spelling, Chinese translation, part of speech (POS), and pronunciation. During the interviews, the learners noted that their MBD use mainly depends on the current task and their motivation to acquire a specific word for future use. The vocabulary test results verify the effectiveness of all three types of MBDs for incidental vocabulary learning in the short and long term, though retention weakened significantly over time. More specifically, while the English majors performed better on the vocabulary tests, the non-English majors made more significant progress. The monolingual group performed better, while the bilingualised group made more progress. The attitude questionnaire and semi-structured interviews addressed five key themes: (1) learners’ motivation for reading and vocabulary learning when using MBDs, (2) learners’ attitudes toward the effectiveness of MBDs for reading, (3) learners’ attitudes toward the effectiveness of MBDs for vocabulary learning, (4) learners’ overall evaluation of MBDs and (5) learners’ satisfaction with MBDs. The bilingualised group was the most positive, especially compared to the bilingual group.

This study refines three strategies of MBD use by Chinese EFL learners: (1) the “so called relevance” strategy, in which MBD use is driven by the task type, goals and difficulty; (2) the “choose the first definition” strategy, which highlights learners’ preference to seek a word’s first definition; and (3) the “availability principle” strategy, which emphasises learners’ tendency to read the L1 equivalents. This study also highlights the importance of (1) L2 authentic and contextualised information as well as (2) repetition and elaboration in learners’ incidental vocabulary learning. Furthermore, this study identifies discrepancies between learners’ MBD use and their attitudes, analysing both micro- and macro-level factors. An ecological model is proposed to provide researchers, teachers and learners with a holistic ecological view of MBDs, which contributes theoretically to understanding the complex, interactive, dynamic and developmental nature of incidental vocabulary learning in the digital era.

As an interdisciplinary study, this research fills theoretical and empirical gaps in the study of MALL, offering language teachers ways to help learners increase awareness of their vocabulary learning problems and to provide guidance in MBD selection and use. In the future, designers and developers could consider making MBDs more personalised, adaptive and interactive.