@Grand Denois
Because of this I wrote "...every country with a first rate mechanical economy and own nuclear plants...".
@.pt
Do you compare the technological abilities of NK, China and other developing countries to Germany and Japan?
We have nuclear test centers and reactors for decades. If one of the western developed countries, especially Japan or Germany with their high developed mechanical industry, decide to put all their efforts into developing an own nuclear weapons program, do you think they would not need just some month for some high-tech nukes?
We have all the tech like centrifuges, nuclear test reactors and normal reactors, ultra accurate milling machines, the best alloys, bomb and missile factories, engineers and scientists. One of our Tornado Wings regularly trains with US B-61 bombs, the european space agency has its headquarter in Germany, we are part of the Ariane transport space program, not small parts of the ISS are from Germany. Japan has its own transport rockets for sats.
What else do you need?
The problems of NK and Iran now and of Pakistan and India in the past has been that they were not able to build the accurate machines and produce the quality alloys needed for good nuclear weapons.
Countries like Japan, Germany, Sweden, Australia, etc. have the companies beinjg able to do this in an easy way.
Not to talk of the resources available if some of the biggest economies in the world begin to focus on developing nuclear weapons and transportation systems.
It is not the question of Japan is able to get nuclear weapons in a very short time. The question is, do the want them?