I always thought that actual actual language proficiency, and language exams go hand in hand. If you pass a high-level exam, you should be able to get by (at least). in that language in a native environment. JLPT is tricky in this aspect, since it has no production part (oral, writing), but I think that this only applies to people who are not good at production to begin with. I would think that most people should have no problem with production, even if it's not tested. The actual capability might be lower than the tested skills, but at least the JLPT works in this respect: If you've passed, let's say N1, you should be able to speak/write at least on a N3 level, even if it was never officially tested. Just my 2 cents.
