For many decadees, The Japan Radioisotope Association (JRIA) has voluntarily translated ICRP publications into Japanese. Going back to what is now known as ICRP Publication 1 The 1958 Recommendations of ICRP, approximately half of the ICRP Publications have been translated. These are available through the JRIA Bookshop.
Now, JRIA has kindly made freely available Japanese translations of several key ICRP Publications: ICRP Publications 60, 103, 109, and 111. Each of these are available for free download through the ICRP web site.