The name - Sea of Japan (Japan Sea) is the only internationally established name for the sea area concerned. The name - Sea of Japan (Japan Sea) became recognized internationally by the early 19th Century during which Japan had been in a state of national seclusion.
(Reference 1:The establishment of the name - Sea of Japan (Japan Sea) )

Countries such as the United Kingdom and the United States use the name - Sea of Japan (Japan Sea) for making their nautical chart. This is because the name - Sea of Japan (Japan Sea) is established in the guidelines on names of seas, published by the International Hydrographic Organization (IHO) entitled "Limits of Oceans and Seas" to which countries in the world refer when making nautical charts.
(Reference 2: The name - Sea of Japan (Japan Sea) established by "Limits of Oceans and Seas" ).

동해를 'Sea of Japan' 이라고 표기함.