joint declar govern kingdom belgium feder republ germani french republ italian republ grand duchi luxembourg kingdom netherland time sign protocol interpret court justic convent septemb jurisdict enforc judgment civil commerci matter wish ensur provis appli effect uniformli declar cooper court justic organ exchang inform decis made court tribun mention articl protocol applic convent protocol septemb wit whereof undersign plenipotentiari affix signatur protocol luxembourg dai june year thousand hundr seventi