The Enlarged Board of Appeal of the European Patent Office stated in the decision G04/08, published in November, 2010 (Official journal of the EPO 2010, p. 572 ff.) that any change of the procedural language is not possible when an international application is entering the regional phase, if the PCT application was already filed in one of the official languages of the EPO and said language was used during the international proceedings.
Dr. Barbara Engels