From April 1, 2019, the JPO will accept PCT applications in Japanese as a subject of PCT collaborative searches for applications where the Japan Patent Office is the main international search organization.
This makes it possible to use PCT collaborative search at a search fee that is cheaper than that for English applications. In addition, it is necessary to submit an English translation (not disclosed) within one month from the provisional acceptance of the application.
Patent Office
https://www.jpo.go.jp/system/patent/pct/seido/pct_kyoudouchousa_shikou.html.