Patent applications (excluding PCT application; please see the above section C for PCT applications) to the JPO can be filed in English. In this case, a Japanese translation of the application must be filed within two months of the filing date.
However, it should be noted that this rule does not apply to applications filed under the national phase of the PCT. In other words, when time is pressing, applicant can file in English for applications with the Paris Convention priority, but not for PCT applications.
If applicant files an application in English, amendments can be filed later for any mistakes in the Japanese translation. For this reason, many Americans think English language application is better than Japanese language application in case of any mistranslations.
However, Japanese patent attorneys generally do not encourage applications in English.
This is because a mistranslation in itself can become a reason for rejection. When considering the difference between English and Japanese, it is nearly impossible to create a truly precise translation between these two languages. Anyone who is interested can claim invalidity of the patent right by pointing out trivial mistranslations.
Also, amendments for mistranslations are not always granted. When filing an amendment, it is required to explain in detail why the mistranslation occurred. As a result, the Japanese patent attorney will have to explain how incompetent he or she is. Moreover, since the other party is very likely to reject any amendment for such a mistranslation, applicants may end up wasting their time in the attempt.
For these reasons, we recommend that applicant file applications in Japanese instead of English if there is any extra time. It is not considered a liability to the applicant because, even if the application is in translated Japanese, obvious mistranslations with respect to the entire specification context can also be corrected in this case.