4. Language used in the taking of evidence 

When the evidence is being taken, a party, witness or expert who is unable to express himself adequately in English, French or German or in any other official language of the contracting states is permitted to use another language. The EPO is responsible for interpreting into the language of the proceedings, assuming that this is necessary, if the evidence is taken at the request of the EPO itself. However, if the taking of evidence follows a request by a party to the proceedings, the use of a language other than English, French or German is allowed only if that party provides for interpreting into the language of the proceedings or, at the discretion of the EPO, into any one of English, French or German. This discretion is exercised in opposition proceedings only if the other parties agree.