Argentina
Lobisón is the word that stands for Werewolf in north Argentina.
The Lobisón is usually the seventh son in a family (whereas the seventh daughter is doomed to be a witch). When they turn into a hairy creature that resembles both a man and a wolf, the Lobisón (a legend greatly influenced by the Brazilian traditions), wanders in the hills and mountains, feeding mostly upon carrion. However, if they get to meet with a human being, they will instantly attack. The survivors (men and women) will then turn into Lobisones themselves, but it is quite rare, because most people die in the claws and teeth of these ferocious creatures. It is also said that if a Lobison's saliva sprinkles over a man or a woman, he or she will eventually turn into a Lobisón.
(thanks to loboazul for the above information)

In the early 1900s the legend of the 7th son (it had to be 7 boys in a row, no girls in between) transforming himself into a werewolf was so widespread and believed that it was causing a lot of children to be abandoned or given away for adoption, and it is said that in some cases the parents killed their own son. Because of this, the president passed a law in the 1920s by which the 7th son of a family automatically receives the godfathership of the president of Argentina! Through this, the state gives him a gold medal on the day of his baptism (when the president officially becomes his godfather) and a scholarship for all of his studies until his 21st birthday. Supposedly, this ended the phenomenon of people condemning their children for fear of the werewolf. The law is still in effect, and it is popularly known, and the presidents have always attended at least some of the baptisms, especially during election season.
(thanks to Rodolfo C. Ferioli for the above information)

Brazil
In Brazil, A humam only will become a "lobisomem" if he was the 7th children (male) from the same father and mother. He changes into a "lobisomem", for the first time when he is 13 years old. Just for two hours: from Midnight to 2:00 am. Always on Friday during Lent.

In some places of Brazil (Portuguese colonization is responsable for the legend in that Country), the damned man changes in a crossroad, friday night (usually the 13th), after midnight when the moon is full.
(thanks to Daniel do N A Bento and Marcio de Paiva Delgado for the above information)

Finland
The Finnish werewolves are rather melancholy creatures (surprisingly...). In our stories/legends/myths  a person usually turns into a wolf without really wanting it, accidentally (by doing something that'll turn him into a wolf without knowing this might happen) or because some witch has put a spell on him (according to Finns, these witches would naturally be Sami, although the Swedes thought we were pretty good at magic ourselves). The werewolf (who's usually bound to be a wolf for nights and days until something releases him from the spell) then lurks around houses, sometimes eating cattle but rarely people and waits for somebody to recognize him. When somebody does (e.g the wolf's mother), she/he can break the spell by calling the werewolf by his Christian name or giving him some bread to eat. Sometimes after the werewolf had regained his human form, he would still have his tail till the day he died. Some houses actually exhibit sauna benches (or whatever they are called; 'lauteet' in Finnish) that have a hole in them, presumably cut for the ex-werewolf's tail. Finland's southern neighbor, Estonia is also known for its werewolf legends. Estonia is sometimes called 'Viro' in Finnish, and at one time werewolves were called 'vironsusi' ('Estonian wolf') in Finland. It should be mentioned, though, that 'vironsusi' is originally the same word as 'werewolf', meaning 'man-wolf' and connecting it with Estonia is a false etymology due to Estonia's reputation as a werewolf country.
(thanks to Riikka for the above information)

Mexico
The werewolf is basically a universal myth. In Mexico, the most widely spread version of the werewolf is the one called "nahual", which comes from the Nahuatl (the ancient language of the Aztecs, becoming thus, the universal language in the pre-Hispanic world)word "Nuahualli", meaning warlock. Since the Spaniards did not bring much on werewolves after colonizing Mexico, the ancient local legends on the subject became predominant. The nahual was a warlock who had the capability to shape-shift at will into an animal, preferably a black or dark coyote. It was believed in the pre-Hispanic times, that people were constantly threatened by these evil beings.

Even if the Spaniards who came to Mexican lands in the mid 1500s were not concerned about werewolfery, they were influenced by other European countries that had pretty strong legends on the subject. And so, this allowed for the nahual myth to survive the Colony times and make its way through present time. Some indigenous groups still currently believe that nahuales turn into coyotes or other animals at night, through the use of magic and sorcery, in order to harm other people. Once they have shape-shifted, nahuales can run the lengths with no difficulty to steal corn of chickens, and to fight other nahuales that pretend to invade their territories. Such indigenous people's legends say that once in animal form, they can get killed if wounded, but in case they survive, they will show the wounds or damage done suffered while in animal form

According to modern-day Mexican indigenous beliefs, the nahuales can shapeshift by performing anyone of the following: Jumping over a wooden cross, getting into deep sleep, putting on an animal skin, or covering their bodies with an ointment made of herbs, Not everyone can achieve the transformation. Just a few ones have been nature-granted with the capability to perform the change, but they also need to be skilled warlocks or sorcerers. These legends also tell about the way to kill a nahual or Mexican werewolf: Stoning, or gun-shooting; they can also be killed by using holy water, fire or by hanging them.

In the Mexican state of Tlaxcala, in the surroundings of the mountain known as La Malinche (the wife of the Spaniard conqueror Hernán Cortés)the nahuas (a local indigenous group) believe that witches or "tlahuelpuchi" turn into fearsome coyotes at night, in order to break inside the houses where small children live to suck their blood. On the day after, parents will find their sons or daughters dead, with savage bites on their necks, legs and arms.

To prevent the attacks by tlahuelpuchi witches, parents leave by the bedside in the kid's room a mirror reflecting the sleeping child, a knife or a pair of scissors, all of which are said to have magical properties that scare-off these savage female werewolves.

In the Mexican state of Oaxaca, there are several indigenous groups, having each one similar beliefs of their own. In regards with the werewolf-like characters, the Zapotecs, for instance, say that nahuales are warlocks who shapeshift into ferocious and damaging animals that can produce great evils to people. They believe that nahuales are warlocks who make deals with the Devil in order to be able to turn into coyotes to suck people's blood while they sleep. They can only shapeshift at night. Their powers, according to such legend, include the capability of damaging unborn children, which explains to them why some kids are born dead or with malformations. In order to scare nahuales off, the Zapotecs place garlic on their doors and a knife or a pair of scissors under the pillow.

On the other hand, the Chinantecs, yet another indigenous group living in Oaxaca, also believe in nahuales. To them, nahuales can be both men and women, and they can only achieve the transformation at night, and they get to kill those who see them or even dare to face them. The Chinantecs say that if the nahual is injured in the battle, but manages to escape, on the day after, the man or woman behind the beast will show scars resulting from the wounds inflicted to them while in animal shape.
(thanks to loboazul for the above information)

Norse
The Norse legends claim that one can change shape by wearing the skins of the animal one want's to change to.(also used by other cultures, belt made from a wolf etc.). Loki (the god) often changed and had a lot of skins(including a worm  and a flea skin).
(thanks to ice for the above information)

Portugal
In Portugal, werewolves are called lobis-homems. In the 1400's there was one kind of lobis-homem that was very quite common: The gentle and non-attacking creature. Once fallen under a spell, the lobis-homem would attend a crossroad at night to become a wolf after groveling on the dirt. Then the creature would run into the countryside, howling out loud, without hurting anyone. A shy and sad creature, the Portuguese lobis-homem could be easily recognized, for it was a wolf with a short and yellow-furred tail.

However, there was yet another kind of werewolf in Portugal, with little resemblance to this noble creature. It was the evil and devilish variety, far less-common though, linked directly to the black arts of witchcraft. Evil lobis-homems could be recognized by the shape of their eyes and sometimes because of the presence of the Devil's mark in some part of the body.
(thanks to loboazul for the above information)

Russia
The person wishing to tranform goes into the forest, sticking a copper knife into a tree and dances about while saying  incantations. When this ritual is performed, the spirit of the Wolf will take over your soul.