I wouldn’t worry about how it looks. It looks better to have a full schedule of courses you do well in than more C’s in Spanish. And he should replace the foreign language with a real academic course.
Most colleges list admissions requirements on their websites, and section C 5 of the Common Data Set (just google the college’s name and common data set) lists the required and recommended units of high school requirements, including foreign language. I have been told in person by admissions representatives from selective schools that they consider the level and not the number of years of foreign language. For example, if a student takes Spanish 2 as a freshman and Spanish 3 as a sophomore, then it really doesn’t matter that three years of language weren’t taken. However, if a college requires four units of a foreign language, then generally, level 2 or level 3 does not satisfy the requirement. I say generally because colleges do consider the context for learning: both that of the individual student, including any learning disabilities (explained in the counselor’s recommendation letter at application time), and that of the school: some public schools no longer offer foreign language to level 4. Advice from admissions reps also confirmed advice from @Marian, @mathmom and @skieurope: take five “solids” rather than woodworking. First semester senior year classes can make a difference. If your high school lacks alternatives, you might consider dual enrollment at local community college to fill out the schedule.
Chiming in, here. My personal experience shows that @perseverance1 is right. But if you have any doubt, just call a couple of colleges that your son might be applying to just to confirm. It might make you sleep better.