Hi, I will be visiting Taiwan from 18 Dec to 26 Dec. May I know how is weather there at this timing

If you go to the north part, the average temperature is about 15 to 20 C. It may rain a lot during that time, according to the previous records. Thin sweaters or long sleeved coats are enough. Remember to take the rain gear.
If you go to the south part, you can take your summer coats.