Europe
Bosnia and Herzegovina
It had not been introduced till the very recent days, and it is still not a declared holiday. However, most schools have children wearing masks and it is called No vjetica (Night of Witches).
Germany
It has been introduced only in the 1990s, and now, around 1/5th of the German population celebrated Halloween. "Trick or treat" (Ses oder Saures in German) is increasing in popularity in areas such as the Dahlem neighborhood in Berlin. Still it is not so populr with the elder generation.To quote Wiki : Complaints of vandalism associated with Halloween "Tricks" are increasing, particular from many elderly Germans unfamiliar with "Trick or Treating."
Ireland
People dress up as characters from the underworld. They light bonfires and enjoy fireworks. The city of Derry has the largest organized celebration of Halloween in Ireland in the form of street carnival and fireworks display. They play games like apple-bobbing, where along with apples, nuts and coins are also dropped. Sometimes, coins are engraved in the apples and the children compete to gain the maximum no. of coins through the game. However, Halloween is considered anti-social in Ireland since 31st October is the busiest day for Emergency Services in the year. Firecrackers are banned in the Republic of Ireland, still they are smuggled from Northern Ireland where is is legal.
Romania
Celebration here is based on the myth of Dracula. The character is believed to stay here as many witch trials had taken place. The most successful party in Transylvania takes place in Sighisoara, the citadel where Vlad the Impaler (aka Dracula) was born. The Fodor's travel guide placed Halloween in Transylvania on a list of Top Ten Must-Do-Adventures. People also visit their loved ones' grave and light candles there.
Russia
It is mostly celebrated by the younger generations and are generally avoided by the theaters and libraries. Halloween, being a Western celebration, the Russian politicians and government are trying to remove it from public celebrations.
Sardinia
In Gadoni, torches made of asphodel stems 2-4 m long are carried through the city by the young people at dusk. This symbolizes accompaniment of the wandering spirits far from the town. People put sas Concas de Mortu (Head of the deads), arved pumpkins that look like skulls, with candles inside, out of their windows to keep the evil spirits away.
Switzerland
Quoting Wiki: In Switzerland, Halloween, after first becoming popular in 1999 is on the wane. Switzerland already has a "festival overload" and even though Swiss people like to dress up for any occasion, they do prefer a traditional element, such as in the Fasnacht tradition of chasing away winter using noise and masks.
UK and USA coming soon.