EPO, Enlarged Board of Appeal, 16 February 2010, Decision No. G 04/08
If an international PCT application has been filed and published in one of the official EPO languages, it is not possible to (upon entry into the European phase) file a translation of the application in one of the two other languages. The EPO bodies may not use themselves in the written procedure one of the official EPO languages other than the official language that was used for the application (Art. 14(3) EPC).
Read the decision (in French) here.
Read a summary in English (provided by Bardehle Pagenberg) here.