The purpose of this study is to investigate the relationship between Arabic Language Proficiency (ALP) and expatriate adjustment (EA), and job performance (JP) in Saudi Arabia. In addition, the moderating role of personal and environmental factors is investigated. This investigation employs a mixed-methods research design. The intended audience is the personnel of Saudi Arabia's Higher Educational Institutions (HEIs). A survey was conducted for quantitative data, while interviews were used for qualitative data. CFA and SEM were used for quantitative data analysis, while thematic analysis was used for qualitative data analysis. The results of this study indicate that Arabic language proficiency significantly affects job performance and expatriate adaptation. It was also discovered that several personal and environmental factors contribute to the impact, including language barriers, the workplace environment, training, and support. This study is novel because it examines the effects of ALP on EA and JP in Saudi Arabia, in addition to personal and environmental factors; no prior study of this nature has been conducted in Saudi Arabia. The study is limited to Higher Education Institutions (HEIs); thus, its generalizability is restricted. The study is significant for Saudi Arabia's Higher Education Institutions (HEIs) because it emphasizes the significance of training and support, which would aid in adapting foreign employees, and enhancing their job performance.