Salsabila, J.R., Sumardi, S. and Putra, K.A. 2026. English Self-Efficacy in a Faith-Based Multilingual Boarding School: A Qualitative Case Study from Indonesia. FOSTER: Journal of English Language Teaching. 7, 1 (Jan. 2026), 146-161. DOI:https://doi.org/10.24256/foster-jelt.v7i1.330.