Hi Rita,
Malta is a great place to visit at Chritmas to escape the rainy weather of England. It stays quite warm all year round and most days are pleasant and sunny.
Tha average temperature for December is 17 degrees so not too warm but nice and comfortable. Through the winter it never drops below 10 degrees and never snows. The overall average winter temperature is normally about 15 degrees but sometimes goes up to 20!
I would advise to pack light stuff such as linen and t-shirts but make sure you include some cardigans and jumpers as it can get quite windy too. You could probably get away with wearing sandels, however I would pack some closed toe shoes and maybe some light boots.
I hope this helps you with your packing. If you would like anymore information, please let me know.
Warm wishes,
Cheryl, your editor