Because in some cases, its the only way to acheive the full pokedex. Also, there are advantages for trading from around the world. If you are a breeder, getting Pokemon from a different language game can be a plus because of the better chance of getting a shiny Pokemon. If you don't like to train much, you can trade for the Pokemon you want with somewhat limited trading possibilities. There are several more advantages, but those are just a few. REMEMBER this: You can only trade for Pokemon that you have seen in the wild or in battles. This does not count for Pokemon you've seen in the Battle Frontier.
yes
you have to be close for people around you or go to the global trade center to trade across the world
No, You have to give them for free than you lick their hair.
Global Trade is the exchange of goods and services between countries. Also, global trade could be taken in the context that there are no barriers to trade, thus there is global 'free' trade between countries.
Go to the GTS.
To trade goods with other people
Using the WIFI link in Pokemon, it is possible to trade Pokemon with people around the world.
Since you can trade with people around the world, close to all of them.But some you cant trade.
There are a great many benefits of international trade. International trade ensures that people from around the world get what they need even when their country cannot produce it.
To promote free trade around the world
A place to trade Pokemon with people around the world
shared trade