OJ EPO 1993, 540

In accordance with Rule 1(1) EPC, any party may, when corresponding with the EPO, use any official language of the EPO (English, French, German). Amendments to a European patent or European patent application must however be filed in the language of the proceedings (Rule 1(2) EPC).

This applies equally to correspondence with the EPO as receiving Office, International Searching Authority or International Preliminary Examining Authority under the PCT (Art. 150(2) EPC together with Rule 92.2(b) PCT and Section 104a of the Administrative Instructions under the PCT).