Article 15 of Law 39/2015, of 1 October, on the Common Administrative Procedure of Public Administrations, states that the language of the procedures processed by the General State Administration shall be Spanish. In line with this, the rules governing these procedures require that documents issued in a foreign language by the competent authorities of the country of origin must be accompanied by a translation into Spanish (when they are not issued in that language):
a) By any diplomatic or consular representation of the Spanish State abroad.
b) By the diplomatic or consular representation in Spain of the country of which the applicant is a national or, where appropriate, of the document’s country of origin.
c) By a sworn translator, duly authorised or registered in Spain.
Embassies and consulates (exteriores.gob.es)