It is possible Why so many people have a problem imagining a governing system that is in charge of the entire planet is because they are trying to imagine a new government based upon the existing structure of the old one. For example, in the United States, we have not a democracy but a democratic republic. We don't make decisions for ourselves; rather, we vote for people to make decisions for us. This was an effective system when the United States was first conceived. The population was so dispersed, and communication so difficult, that the most effective form of government was one that localized power to a select few. Fast forward to today. We live in a world that becomes more and more connected every day. Communication is almost instantaneous, and everyone can (with access the proper resources) be "plugged in." Why don't we create a new form of government? One that the citizens vote for representatives, but is also fully transparent. The citizens would have the opportunity to go online to a central "hub" and vote on issues directly. They would have the ability to navigate through local and global issues, and would be able to overturn any political action taken by the representatives by a majority vote. This would help to prevent the corruption that can run so rampant through the systems we currently have.
A global government is possible; and if we want to progress as a species, it is necessary.Also It can work There are 196 countries in the world. That means a parliament/senate if you wish with 196 members. A lot of minds and ideas to make the world a better place. All that remains is to get rid of greed and selfishness. Banks, big oil and pharma companies need to be put in their place.
though it may be possible for people nationwide to contact each other, what has to be taken into consideration is the fact that not everyone on the planet speaks the same language or has the same set of political or social views as others, as for example in the U.S. it is completely legal for someone to participate in what ever religion they so choose, however in countries such as Saudi Arabia religious freedoms are not protected nor recognized politically. As well as a clash in religious views, there would be many political arguments that would form because of the fact that every country on the globe dose not agree with a democratic republic or its practices, because they have their own government forms that if were changed would result in nothing more than civil war between the newly formed super government. Also with the amount of groups that resent the U.N. and the U.S. there would no doubt be war for who holds power and as to what laws are passed because most of them would refuse to have a new form of global government forced on them. Lastly not everyone in every country has access to things such as the internet or simply a computer and it would not be fair in any sense to exclude them from the voting process.
Have you read Orson Scott Card's novels, Shadow Of the Hegemon and Shadow Of The Giant? I recommend you do because the way they set up their world government could be used realistically in real life. As for the language barrier setting up a world government could give people the chance to become multilingual or set up some "new" language for everyone to use as their secondary dialect. The world would be united under one government but it wouldn't be forced, citizens of each country would vote to join to become a part of it if they wanted, the big idea of this is to keep peace, no more war, and to learn from other cultures, its time to stop making enemies. Unfortunately this is the closest thing we'd have to paradise. As for religion it wouldn't change, people would still have the freedom to choose their own religion, and there would be no prejudice against them or anyone else. Also individual countries/regions would still function as they do now(except for ISIS that'll be addressed later) but will be interconnected. Lastly we need to stop thinking about nations and think about our species as a whole because at the rate were all going the human race is gonna make itself extinct.