Translate the following English sentence to French:
"It is urgent that those countries which aspire to join the European Union should be perfectly clear about the changing nature of the acquis communautaire and the regulations that they will have to follow."
Il est urgent que ces pays, qui aspirent à rejoindre l'Union européenne, soient parfaitement informés de la nature changeante de l'acquis communautaire et des règlements qu'ils devront respecter.