None of the above. 1 language would be create for clear communication, but some languages are lacking for words and descriptions of some emotions, events, and dichotomies. 1 World Government shares the same problem as 1 unified religion; in such scenarios there is no alternative option/view that can be offered to find the best way/Truth (this is directly from "On Liberty" by John Stewart Mill). Without the opportunity to compare the current known Truth/understanding to an alternative one, you are robbed of the chance for revalidation of your current understanding, or robbed of the chance to exchange falsehood for truth if your current view is inferior/false. It's kind of like the story of three blind men all feeling different parts of an elephant and all coming up with different ideas of what it actually is. One feels the trunk and says its a snake, one the leg and says its a tree, etc.
What is needed for peace and understanding are several different approaches (Language, Religion, Gov't) that are designed to coexist, adapt, and learn from each other. Just look at the human brain for a good example of harmony. It isn't one single perfectly working brain, but 100,000,000,000 different simple ones all working and competing with each other to evoke understanding and cohesion.