I came to the office since the it was an onsite interview. The tech lead asked about my experiences and technical skills in English to filter if it was fit to the current project and the team. Once the technical interview aspect finished, the CIO (Chief Information Officer) continued to interview me and asked some question in Mandarin. The CIO asked me to answer in Mandarin since most of the time the whole team will communicate in Mandarin. The final decision was based on the CIO.