Thanks to Coop from WoWS global fanbase FB group! He also wrote some description for the flags:
I took a look at the flag file for 5.9, new additions to it, new flags being added to the game.
^Republic of China flag, which given the Anshan and Lo Yang already have their own flags, it must be for another pan asian premium. I would bet money on it being the HMS Aurora which was sold the China and renamed the “Chung King” which WG mentioned was a premium ship they were working on a while back.
Amongst the signal flag section of the file there is a new one with a clearly pan-asian flavour to it: