The Japan Patent Office (JPO) requires that patent applications in Japan must be filled out in Japanese. Furthermore, the title of each document and the headings of each document must also be written in Japanese. While the actual description, claims and drawings may be originally submitted in English, the JPO will require Japanese translations to be submitted within one year and two months from the earlier of either the filing date or the priority date. If the translations are not submitted, the application is deemed withdrawn.
Before filing for patent or utility model protection in Japan, it is advisable to keep the patented material secret, or at least unpublished. If the material you wish to patent has already been published elsewhere, it will have lost its novelty and will no longer be patentable in Japan. However, an exception exists for material patented in other countries that fit specific criteria.