Where the certified copy of the previous application whose priority is claimed (priority document) is not in an official language of the EPO, a translation into one of those languages need only be filed at the invitation of the EPO. This invitation is issued only where the validity of the priority claim is relevant to determining the patentability of the invention concerned.

With the exception of amendments to the European patent application or European patent, any party may use any of the EPO's three official languages in written proceedings before the EPO.[Rule 3(1); ]

The official language of the EPO (English, French or German) in which the application is filed, or into which it is subsequently translated, constitutes the "language of the proceedings".[Art. 14(3); ]

The language of the proceedings is the only language used by EPO departments in written proceedings on that application (see G 4/08).

Where European patent applications are filed in one of the official languages of the EPO, or after they have been

European divisional applications must be filed in the language of the proceedings of the earlier (parent) application. Alternatively, if the earlier (parent) application was not in an official language of the EPO, the divisional application may be filed in the language of the earlier (parent) application.

European patent applications can be filed in any language.