China's slump

 The last time China's inflation was so negative was during the GFC (global financial crash), and before that in 1998/99 (the Asia crisis)  And yes, inflation is negative, i.e., consumer prices are falling.  This is called deflation, and is a sign of extreme economic weakness, but is also very dangerous in an economy with as much debt as China's.  Deflation means incomes and turnover are falling, but debt doesn't fall.  The only way to cut debt is to repay it from your profits or income, and as income/sales fall, this gets progressively harder, leading to more bad debt, more defaults, and further declines in the economy.   When this happens, it's called a debt-deflation, and it was a key factor in the collapse during the Great Depression from 1929 to 1933.

In the past, China has always averted this by encouraging investment in plant and equipment and in housing.    But her population is falling, so housing stimulus is unlikely to work.  House prices are falling, and housing investment is collapsing, leading to spectacular bankruptcies by giant property developers.  Many people have bought houses "off the plan" and are now paying mortgages for flats which will never be built.  Meanwhile, erratic policy towards the private sector is discouraging foreign investment, while domestic fixed asset investment continues to slide.   And it seems that until very recently, Xi doesn't appear to have been concerned. 

China matters.  Even though the official GDP data are very rubbery, it is prolly the world's second-largest economy with ~15% of world GDP, and it is also the world's largest importer of raw materials.

Falling prices in China is a clear sign that economic growth is much less than stated, and that the economy is in a slump.