For admissions, the foreign language classes he is taking would be more beneficial. If he wants to use the native language to fulfill college language requirements, he can take the AP test, but the SAT Subject Test is a cheaper option, and the college’s placement exam is cheaper still.
Now, let’s suppose that this student is one that falls into the 0.1% of applicants. If the student is fully proficient in a language other than English, and the HS does not offer appropriate courses for him in the LOTE, so the student opted to take a different foreign language and quit after 2 years, then it’s probably OK. However, in one-off cases such as this, the student really should speak to the GC and his target colleges to confirm.
Remember, most of those colleges that make recommendations for HS preparation know that they are one-size-fits-most, not one-size-fits-all. Obviously there are unis like the UCs for CA students, where “required” means “required,” but those are the minority.