A big part of the population in Malta is foreign, it's very common to see foreign plated cars. Malta has these rules as well but are not really well enforced, they sometimes clamp foreign vehicles parked on the street but they never ask questions going in and out the country with the ferry or when driving around in Malta you never get stopped for having a foreign vehicle.
European plates don't attract attention what so ever, non EU plates might raise more questions,︀ especially from customs etc.