@BefuddledMom is your son still dealing with health issues now? Does he have chronic issues that will follow him to college and require accommodations from college disability office?
If his medical situation is uncertain, and there is likelihood of repeat flareups, I would be cautious about trying to squeeze in extra summer courses for foreign languages. I would suggest just trying to get regular workload done. Admissions Counselors can learn of extenuating circumstances through student, or guidance counselor. Unless you are shooting for tippy top level colleges, some strong teacher/guidance counselor recommendations can assure college reps of your son’s intellect and work ethic.
If you cast a wide net of possible colleges with solid cs department, you should be able to find one that will accept your son’s high school transcript as is.
My D applied to an OOS public university, well regarded but not in top 20, and they had a requirement for 3 years of the same foreign language. They accepted my D’s 2 years of Latin, 2 years of Spanish without any hesitation.