I’m fluent in Chinese and am in 8th grade right now. My parents want me to take a lot of AP course but I crack under pressure easily. I know that self-studying is a thing and that people can take AP exams in junior/ senior year without taking the actual class. I want to take the Chinese AP exam during summer break or in freshman year. Is that even possible?
AP exam schedules are pretty set for May. I’m not sure if you, as an 8th grader, can take it in May.
Does your school offer Chinese? If so, then take it as a freshman and then take the test in May.
If it doesn’t, talk to your high school GC next year about how to go about taking the AP test.
There is no benefit in taking the test early. Like the above poster said, they are only offered in May.
Your parents need to be aware that no college thinks that APs are an arms race where the one with the most wins. As an aside, I can’t help but wonder how many APs they took in HS 
To clarify an earlier answer, yes, one can take an AP exam as an 8th grader, although the student would need to find a test center to order the exam. Whether you should take the exam this year or wait until next year is another question.