Classes/courses that count as college credit outside of college?

Most colleges will allow you to receive credit for some classes by "testing out" of the class. That is, you take a test similar to the semester final in a given subject and, if you pass, you receive credit for that course.

Many courses are covered by a well-known "testing out' program known as CLEP (see source, below). I believe they test for Spanish, French, and German, but I don't think they test for Japanese. However, even if a course is not included in the CLEP testing, some schools will give you their own test. Sometimes, if you pass, those tests result in actual credit begin granted; other times, those tests simply allow you to be placed into a more advanced-level class. These policies and procedures vary, according to each individual school.

If you have a school in mind, call them to ask whether they would be willing to grant college credit for "testing out" of Japanese. If so, you could study independently and then test out when you get to college.

If you study independently and learn Japanese, then take it while at college, the courses would no doubt be easy for you to pass -- assuming you learned it correctly in the first place.

Good luck!