<![CDATA[This study aims to analyze the forms, causal factors, and implications of regional language interference in Indonesian-language Friday sermons through the perspective of cross-cultural communication. Friday sermons serve as a vital mass communication channel for transferring religious values; however, the linguistic dynamics in multilingual urban-suburban mosques frequently exhibit structural mixing. This qualitative study employed a descriptive case study approach. Data collection was conducted through non-participant observation, digital audio recording, and semi-structured interviews with six preachers (khatib) and ten congregants from various cultural backgrounds in West Java. The collected data were analyzed using the Miles and Huberman interactive model. The results indicate that regional language interference occurs systematically at the phonological, lexical, and syntactic levels, predominantly driven by Sundanese and Javanese language structures. This interference is caused by the proximity of the preachers' mother tongue, psychological efforts to establish cultural intimacy, and situational demands to clarify complex theological concepts. In the cross-cultural communication perspective, regional language interference serves a dual function; on one hand, it successfully enhances emotional resonance and proximity for local congregants, but on the other hand, it triggers cognitive anxiety and decoding blockage for migrant congregants due to linguistic uncertainty. This research implies the importance of preachers balancing cultural contextualization with linguistic inclusivity to optimize the absorption of religious messages within a multicultural congregation.]]>
