Teaching Indonesian in overseas elementary schools involves navigating multilingual realities rather than introducing a completely new language. At Sekolah Indonesia Cairo (SIC), students generally demonstrate functional proficiency in Indonesian as the language of instruction, while being consistently exposed to Arabic in their daily environment and English as an additional school subject. This study examines how cross-linguistic influence, particularly from Arabic, shapes students’ pronunciation and writing in Indonesian, and how these patterns can be meaningfully addressed in classroom practice. Using a mixed-methods approach, data were collected from 32 upper-grade students through speaking tasks, writing activities, classroom observations, and teacher interviews. The findings indicate that phonological variation occurs in systematic patterns, including consonant substitution, vowel shifts, epenthesis, and deletion. These patterns are closely related to orthographic representation, suggesting that students’ perception and production of sounds continue to shape their writing, even at relatively proficient levels. Rather than interpreting these patterns as signs of deficiency, this study positions them as part of a dynamic multilingual repertoire. From an ethnopedagogical perspective, the findings can be understood across linguistic, pedagogical, and cultural dimensions, highlighting the importance of integrating students’ linguistic patterns, learning processes, and cultural backgrounds into classroom instruction. By designing learning activities that connect pronunciation, writing, and meaningful cultural practices, teachers can support more adaptive and context-sensitive language use. This study offers practical insights for Indonesian language teaching in multilingual elementary classrooms.