Hi johannesbittag ,
Actually I did understand you, but you can not let customer chose with MI - that front end experience was not yet developed.
One workaround is to setup two shipping zones and actually automatically offer the customers that come from Europe the Netherlands shipping charge and delivery time. When that is depleted even the customers from Europe will get the China option. Let me show you how to set this up:
You need is to setup two shipping zones and add different shipping method to both.
So zone 1 add Europe countries - shipping method 2 days 4 euros
and zone 2 add all other countries you allow (sorry but WooCommerce does not have the rest of the world option I believe) - shipping method 14 days 15 euros
Then you go to ATUM - Settings - MI
Region Restriction - shipping zones (your clients will have the option to add their address to the side bar or use geo prompt as explained below). According to zone customers are in the correct stock is shown.
Default shipping zone use - China as you said you have always some stock in there
Inventory Selling Priority - Manual
Inventory Iteration - use next in priority order.
Expirabe Inventories - not sure if you need?
Price per inventory - again not sure if needed?
Use Geo Prompt - on and set it up if you need.
Hope this helps.