first language

Although he works in English, Spanish is his first language and he speaks it at home with his parents.

(Chinese) 尽管他用英语工作，但西班牙语是他的母语，他在家里和父母说西班牙语。

Educational researchers debate whether science should be taught in a student's first language or in English.

(Chinese) 教育研究人员在争论科学课应该用学生的母语教授还是用英语教授。