Language interference is a phenomenon caused by bilingual or multilingual society. Language interference is common in the second language due to the influence of first language of speakers. In the islamic boarding school community, Javanese is often used by the community everyday. Additionally, Arabic is also quite dominant in daily for learning religious literature. Religious literature which almost uses Arabic is described by Javanese to get the meaning. The Javanese which is written by Arabic characters is called by Arab Pegon. Then, Javanese and Arabic usually interfere the use of Indonesian in a public speech of islamic boarding school community. Interference in the speech can bring language shift, if it occures together and con...