Since east sea is between Korea and Japan, still lot of people get confused to using the right expression, east sea. However, once Korea and japan agree on a common disignation, this could be seen as an accord with the rule of international cartography and we should follow it.
Also it is Korean citizen's duty to correct wrong expressions and announce right expression for Korea's territory, especially East Sea.
Correcting 'Sea of Japan' to 'East Sea' is not just correcting several words, it is the action of following general rule and making the website improve.
So I urge you to use 'sea of japan' and 'east sea' together so that users of your website could consent more on your website and have right knowledge about this.