While previous interventional studies on English as an international language (EIL) have focused on the role of teachers, recent studies have begun viewing how students engage autonomously in informal digital learning of English (IDLE) activities that are associated with their perception of English varieties and cross-cultural communication strategies. This mixed-method study examined the empirical relationship between IDLE and these two aspects of EIL involving 324 Indonesian EFL students. Results showed that receptive IDLE activity (e.g. watching English content) significantly predicted positive perception of English varieties, whereas quantity (frequency) of IDLE and productive IDLE activity (e.g. communicating with English users) significantly predicted the development of cross-cultural communication strategies. This study sheds light on the emerging phenomenon of how contemporary EFL students are exposed to and interact with diverse forms, accents, and users of English in a range of IDLE environments, along with the pedagogical implications for ELT. Copyright © 2019 The Author(s). Published by Oxford University Press; all rights reserved.