BDAttitude's information is correct. France, for instance, will only accept such an aircraft if it has been wholly built by the original manufacturer and the same for all subsequent modifications and ADs (the manufacturer's official agents are included). But it will be a risk just the same.
With regard to dutch aeroplanes: it is no different because there are no international agreements for ULMs/Microlights/LSAs, call them what you will, including within the EU member countries. There are a large number of dutch registered ULMs in France and most likely throughout the EU but they remain on the dutch register - extremely risky. This is achieved by the dutch seller agreeing to keep your aeroplane on the dutch register with their name and dutch address pretending they are still the owner. A number of dutch sellers offer this as part of their sale agreement but there is nothing to stop them changing their minds later.