We wouldn't say it because Chinese don't celebrate Halloween!
There is no translation for "trick or treat" in Chinese because Chinese people traditionally do not celebrate it. However, quite often (in English speaking countries), if you say "trick or treat" in English, people (even other ethnicities) will generally understand it.
TRICK OR TREAT, mon
knock on someones door and say trick or treat
if you dont get a treat you do a trick on the one that didnt give you a treat
just say trick or treat in a nice way
In the USA it's generally just that, "Trick-or-Treat".
Trick or treat!
Nous sommes allés trick or treat
Trick or treat in French is friandises ou bêtises.
You say trick or treat when you arrive at a house on Halloween so the owner will give you candy and you won't have to play a trick on them. You say thank you when they give you candy because it is good manners.
I will knock on peoples doors and say " Trick or Treat ". We receive candy! =) What a fun way to get candy.
Hermione never says trick or treat in either the books or movies.