Sー23 is the guideline for illustrate chart to explain each Zone of the sea and oceans.

You can check it in the IHO website here http://www.iho.int/iho_pubs/IHO_Download.htm
Check the downloaded PDF http://www.iho-ohi.net/iho_pubs/standard/S-23/S23_1953.pdf
PDF page 34. Article 52 "Sea of Japan".
Also , check it on IHO hydrographic map here.

The Defenition of "Sea of Japan " is as follows on S-23
52.-Japan Sea/
 On the Southwest
   The Northeastern limit of the Eastern China Sea (50) and the Western Limit of the Inland Sea (53.

 On the Southeast
    In Simonoseki Kaikyo
    A line running from Nagoya Saki (130"49'.05E) in Kyusyu through the island of Uma Sima and Muture Sima (33"58'05 N) to Murasaki Hana (34"01' N) in Honsyu.

 On the East
   In the Tsugaru Kaiko
   From the extremity of Siraya Saki (141"28' E) to the extremity of Esan Saki (41"48' N)

 On the Northeast
   In La Perouse Strait (Soya Kaikyo)                                 (Click here on google map)
   A line joining Soni Misaki and ishi Notoro Misaki (45"55' N)

 On the North
   From Cape Tuik (51"45.7 N) to Cape Suchcheva.

The claim made by South Korea is originally they want to rewrite this Chart and guideline, From Grobal standard name of Sea of Japan into  Korean ethno-centristic selfish name of "East Sea", though the "East Sea" is not match with the difiniatin of "Japan Sea" definiation on S-23. "East Sea" by Korea was originally just a east coast of Korea. East Sea is just a part of Japan Sea, or just a east Coast of Corea a.k.a broughotn bay rather than Sea of Japan area which shows in the IHO S-23 No.52 area above.

Sea of Japan is reasonable name for hydrographic studies because of following reason;
Japan islet separates "Sea of Japan" and Pacific Ocean.if there are no Jpaan islet, "Sea of Japan" is not exist and it is just a part of Pacific Ocean So it is "Sea of Japan

Also, Korean peninsula separates Sea of Japan and East China Sea.  If there are no Korean Peninsula, "Sea of Japan" is not exist and it is just a part of East China Sea. So that is why it is "Strait of Korea".

Limit of Oceans and Seas / Lmits des Oceans et des Mers