Bulgaria will be the next country to ratify the UPC Agreement according to the UPC Preparatory Committee which expects the ratification to happen by the end of April.
Bulgaria would then become the 10th country to ratify the UPCA ( Austria, Belgium, Denmark, Finland, France, Luxembourg, Malta, Portugal and Sweden have already ratified). To enter into force the UPCA must be signed by 13 countries including France, Germany and the UK.
See our ratification table here and all the news about ratification here.