This case study investigates the intricate interplay of multilingualism, specifically in Chinese and English, and its consequential impact on the language of instruction in the context of teaching Indonesian as a foreign language in Taiwan. This research delves into the nuances of language pedagogy within a multicultural and multilingual educational setting. This study employs case study methodology, gathering data through classroom observations and openended student questionnaires. Additionally, students' progress, as evidenced by assignments and feedback, serves as a quantitative indicator to measure the influence of multilingualism on their language learning journey. Key objectives include examining student preferences and perceptions on the use of Chinese and English in Indonesian language course instruction. The research explores instances of code-switching and code-mixing, shedding light on the dynamic language choices of instructors and learners. Through an analysis of student progress, the study aims to discern tangible outcomes associated with the multilingual approach. The results show that students found the classroom dynamics positive and motivating, enhancing their learning experience. Local students benefited from using Chinese, while international students appreciated the multilingual approach, though some noted occasional delays in translation. Overall, the study provides insights into the benefits and challenges of multilingualism in Indonesian language instruction in Taiwan, contributing to discussions on effective practices in multilingual education.