How do I prove I am major/minoring in a foreign language if I’m not yet in college, or can’t declare a major/minor until Sophomore year?

If you are currently a college student your transcript, which you need to submit along with the application, will list your major/minor and the course(s) you have already taken - thus, verifying that you meet the qualification.

If you are currently in high school and are going to college next year there are several alternatives to verify your major/minor. If you have a letter of acceptance from the college/university it should show your planned major/minor; or, if you don't have that, then a letter from the admissions person you are working with at the college/university, stating your intended major/minor, will do; or, finally, if neither of those are available, you can have your high school guidance counselor write a letter indicating the language you took in high school, and your intended major/minor language in college.