certifcate 39
Maybe it is this requirement:
People who have taken a divorce within the European Union are required to attach a divorce certificate with an official translation, issued by the competent authorities in accordance with the Annex to art. 39 of the Council Regulation (EC) No 2201/2003
The law:
Article 39
Certificate concerning judgments in matrimonial matters and certificate concerning judgments on parental responsibility
eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32003R2201