But the rules do allow it.
Japan is in the Asia Pacific region.
The fact that POP does not run events in Japan is beside the point.
For the World Championship (and LCQ), players from Japan, in the Asia Pacific region ARE playing in a POP tournament and therefore that rule applies to them.
When they are in Japan, playing in an event run by Creatures, they play by Creatures rules.
When outside Japan, they play by POP's rules. And then, English cards are legal for them.
Simple as that.