Could he take Mandarin 1 junior year, then dual enroll in College Mandarin 1&2 senior year? That’d cover the requirement since College Mandarin 1 covers HS 1+2 and College level 2 covers Level 3. It’d also set him well for any college placement.
Depending on the college there may be a foreign language requirement he’ll need to fulfill and the combination above would either get him done or require just one more semester.
Chinese is MUCH MUCH more difficult than Latin, so that it would take about 2 years to learn what he learned in Latin over 6 months (US Defense classification). It may be more efficient to pick up a spoken language, such as Spanish, French, or Italian, that has common roots with Latin (all three are easier than Latin.)
In order to get a “useful” level in Chinese, he’d need to take it all 4 years in college and study abroad for a semester.
The most selective 4-year colleges expect 4 years or AP, but most selective colleges will expect 3 years.
Can he take “regular” or “conceptual” Physics next year? He’d then take AP CS senior year.
The usefulness of the 5 core subjects is the way they stretch and challenge the brain, rather than their practicality. Then, the 6th (or 7th) class can be something that reinforces an interest or prepares for one’s major, etc. That’s where AP CS would fit in.
Your son should definitely take AP Econ (micro¯o), AP English Language, AP Gov. Then as a non core class, AP CS.
Completed with a math class and a foreign language class (dual enrollment if offered).