False attribution. You think Japan's woes are only due to its low birth rate? It's due to the fall out from the plaza accords, and they never recovered. Their industries failed to be competitive after the real estate bubble burst, which was a result of the currency changes from the plaza accords. They're government allowed US companies to steal their tech secrets and made them limit exports.Japan is not unique, it's just ahead. Demographic crisis that China is going to face shortly is going to be far more severe than Japan. And China is so large that there aren't enough countries that can even supply it enough immigrants.
Trying to bring in birth rates at the main cause is disingenuous.