Deflation is a symptom, not a disease. Treatment, if necessary, should be directed at the disease, not at the symptom.
IMO, Japan's deflation is a result of their failure to keep up with any of the emerging tech from the late 90's onward, falling behind in cutting edge computing, software, smartphones, renewables, EVs, etc. They responded to this by holding onto the aging industries they're good at for dear life, resulting in a society that still relies on them (e.g. ICE vehicles, fax machines, etc.) and an industry that's very good at building them for cheaper and cheaper cost. Throwing cheap money has not worked because corporations realize these old tech have no future, and instead of investing the cheap money at home resulting in the virtuous cycle of rising wages -> rising prices -> rising profits -> rising wages they hoarded cash or invested them elsewhere.
In China, IMO deflation is the result of a shifting internal as well as global economic and trade structure. The property market, while a deck of cards, is something the average Joe could invest in and profit from. The booming renewables, EV, and semi market, while more substantial and enduring, is not yet something the average Joe feel confident in investing due to the volatility and immaturity of the Chinese equity market. This hurts consumer confidence. Then you have the falling commodity prices due to coming off of highs of the COVID era and the falling demand from the West from a combination of stagnating economy, trade barriers, and also coming off of COVID highs.
These are different diseases, and require different treatments. Artificially raising inflation by pumping money into the system will do nothing long term. For Japan, they need big structural changes to catch up to new and emerging tech. They've been talking about it for decades but nothing substantial has been done. For China, there needs to be a way to allow individuals to confidently invest in domestic corporations. Whether that's through reforms to the stock market or establishment of intermediary government-backed funds I don't know, but there needs to be a way to better mobilize Chinese citizens' capital. The commodity prices and foreign trade is cyclical and nothing needs to more needs to be done aside from what already is being done (e.g. rerouting trade, developing new markets, improving trade relations with Western powers with sticks and carrots, etc.)
