Any party may likewise use one of the official languages of the contracting states, other than English, French or German, on condition that they make provision for interpreting into the language of the proceedings. However, if the parties and the EPO agree, any language may be used in oral proceedings without interpreting or prior notice.[Rule 4(1); Rule 4(4); ]
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/e_v_2.htm
Date retrieved: 17 May 2021