Where the applicant has filed an application in a language other than an official language of the EPO in accordance with Art. 14(2), or the application was filed by reference to a previously filed application which was not in an official language of the EPO (see A‑II, 18.104.22.168) and the question arises as to whether a particular amendment proposed by the applicant or proprietor extends the content of the application or patent beyond the content of the application as filed and thus offends against Art. 123(2), the EPO should normally assume, in the absence of proof to the contrary, that the original translation into English, French or German is in conformity with the text in the original language, which can be any language (e.g. Japanese). However, it is the original text which constitutes the basis for determining such a question. Similarly, it is the original text which determines the content of the application as filed for the purposes of Art. 54(3) (see G‑IV, 5.1).
An erroneous translation from the original language of filing may be brought into conformity with the original languagetext (e.g. with the originally filed Japanese-language PCT application) at any time during proceedings before the EPO, i.e. during pre-grant proceedings and also during opposition proceedings. But during opposition proceedings any amendment to bring the translation into conformity must not be allowed if it offends against Art. 123(3), that is if it is an amendment of the claims of the patent which extends the protection conferred.