First, Japanisches sea is Japanese wrong expression.
Nowdays, Japan make some plans to get the Dokdo island, and the expression of the Japansches Meer is the pre-plan of this. They will argue that Dokdo is their territory based upon the Sea's name. So we should express this quite correctly to East Sea
As you know, Dokdo is our own territory and we don't want to lose it. It has great supplies and Japan always want it. So, the expression east sea has great meaning to us and the first step to make clear about our territory.
Second, for the historical values.
I know the Germany always have some respect to the jews and that's why I respect your country. Our country also have some big hurt to the Japan.But Japan didn't admire their faults until other country know these faults. I'm the part of the Korea and I have some duty to make clear the wrongs so I need your help and I wonder that you will change your mind.
So if you change it to East sea, it will also helpful for correcting historical facts.