To the best of my knowledge only 2% of Japanese practice
That's probably not far off what it is in other countries. It's hard to find good statistics on it though. I did find one survey reporting about 5% of Americans reported practicing a martial art "at least once in the last year." I'd bet the percentage engaged in
consistent practice is significantly lower, though.
Well as you said it's both if we want a better understanding. I guess I always say we.
I apologize, but I'm still having trouble following your meaning. Are you saying that both Japanese need to understand non-Japanese culture and non-Japanese need to understand Japanese culture? I guess I can see how that could be helpful for transmission of traditional Japanese arts to the rest of the world, but what does it have to do with the vast majority of martial arts which are not Japanese?
It would be nice if it was universal but I see so may things written here that bear no resemblance to Japan although people seem to thing they do.
Is this a response to my statement that "martial arts are a universal feature of human culture"?
Martial arts
are a universal feature of human culture, but obviously
Japanese martial arts are not universal. No one should expect the practice of Kali, Capoeira, Glima, Boxing, Savate, Choy Li Fut, Greco-Roman wrestling, Jeet Kune Do, Muay Thai, Bando, Western Fencing, Silat, or thousands of other non-Japanese arts to follow the specific culture of Japanese Budo.
Even most arts which have some historical connection to Japan have gone their own way, based on the local culture. BJJ, Sambo, and TKD have roots in Japanese arts, but they are not Japanese. That's pretty much what you would expect and there is nothing wrong with that.
Tae Kwon Do actually is a pretty instructive example of how the process works. The Okinawans took Chinese martial arts (particularly Fujian White Crane) and fused them with local traditions (Te) to form Okinawan Karate. The Japanese took Okinawan Karate, but put it through their own cultural filter to create systems of Japanese Karate which were visibly different from the Okinawan approach. The Koreans took (primarily) Japanese Karate systems and over time transformed them into a distinctly Korean art.
That does leave those systems of Japanese origin which are practiced worldwide but which are still identified as Japanese, for example Judo, Aikido, and Kendo. Certain elements of Japanese culture and tradition are taught alongside the technical aspects of these arts, but I'm sure those elements as grasped by most non-Japanese are minimal, fragmented, distorted, or outright incorrect in a large percentage of cases. With your background, you are in an excellent position to offer clarification of those elements for those who practice those arts and wish to better understand those parts of the tradition. It's just confusing when you make comments which seem to apply that perspective to martial arts as a whole.