Vertaling van "supposed to have been kept well hidden until " (Engels → Frans) :

In the last two days the leader of the separatists has imprudently let out several secrets which were supposed to have been kept well hidden until after the referendum.
Au cours des deux derniers jours, le chef séparatiste a commis l'imprudence de relever plusieurs secrets qui devaient rester bien cachés jusqu'après le référendum.

We are in favour of the complete publication of all documents, all agreements, all treaties, as well as the details of all the speeches that are currently hidden, all the dealings that are kept secret, all the lobbying activities that have led Parliament, the Council or the European Commission to take a decision or to issue a directive.
Nous sommes pour la publicité totale de tout document, tout accord, tout traité, ainsi que des éléments de toutes les interventions aujourd'hui occultes, de toutes les tractations tenues secrètes, de toutes les opérations de lobbying qui ont amené le Parlement, le Conseil ou la Commission européenne à prendre une décision ou à émettre une directive.