Colleges want to see foreign language study in high school. He should take a new language or continue with higher level college Chinese courses throughout the next 3-4 years.
Ivy admissions: Taking Chinese AP test and SAT II instead of 4 years Foreign Language in high school
^ it’s also very important for you to understand that “Asian boy interested in stem” is on par with “Upper middle class Northeastern girl interested in NESCAC” in terms of “standing out”, IE., opposite thereof.
So, dropping foreign language to take more stem classes won’t help him stand out.
Pursuing one STEM interest to the highest level possible (most likely, through dual enrollment form and/or personal, not necessarily competitive pursuits) is a great idea, but he should make sure he is well rounded and does not neglect clany academic field
(A typical HS schedule has 6-7 periods. Taking each core class -1 each of math, English, Foreign Language, Social science, Science - still leaves 1-2 elective classes for freshman and sophomore years, and 3 Jr/SR years. That’s plenty to indicate academic interests without shortchanging core classes.
PE and Health can typically be taken " online" over the summer if necessary.)