Is this set in the past, present or future? A planet at the equivalent of 2000 B.C. Cannot possibly have a single language for obvious reasons. As time and technology progress, so will the chance of languages re converging.

Rome had successfully made the standard language in almost all of Europe Latin. The reason it was Latin is because the conquerors spoke it, and when they conquered a region they wanted the locals to understand them and learn Latin, and didn't want to learn Gallic. The only Roman areas where Latin was not dominant was Greece, where the locals were already "civilized" by Roman standards and language was similar enough to Latin for administrators to want to adopt. There is a reason that all Western European languages have roots in Latin.

From this we learn something - the leading language has to be the language primarily used to govern.

As technology increases, certain nations are bound to become superpowers (think USA and USSR). These superpowers will each have zones of control where their nation's dominant language turns into their puppet's dominant language. The USSR broke up before puppet nations began adopting their language, but I suspect that if it lasted for another century the primary language in Poland, East Germany, Hungary, Romania, Cuba etc. would be Russian.

To get a one-world language overnight is unrealistic, however creating a dominant language that slowly increases in popularity under a one-world government (also see this question) is extremely possible, even probable.

How you go about creating this government and keeping it in power long enough to effect language is your choice, although the linked questions should give you a few ideas.

Is this set in the past, present or future? A planet at the equivalent of 2000 B.C. Cannot possibly have a single language for obvious reasons. As time and technology progress, so will the chance of languages re converging.

Rome had successfully made the standard language in almost all of Europe Latin. The reason it was Latin is because the conquerors spoke it, and when they conquered a region they wanted the locals to understand them and learn Latin, and didn't want to learn Gallic. The only Roman areas where Latin was not dominant was Greece, where the locals were already "civilized" by Roman standards and language was similar enough to Latin for administrators to want to adopt. There is a reason that all Western European languages have roots in Latin.

From this we learn something - the leading language has to be the language primarily used to govern.

As technology increases, certain nations are bound to become superpowers (think USA and USSR). These superpowers will each have zones of control where their nation's dominant language turns into their puppet's dominant language. The USSR broke up before puppet nations began adopting their language, but I suspect that if it lasted for another century the primary language in Poland, East Germany, Hungary, Romania, Cuba etc. would be Russian.

To get a one-world language overnight is unrealistic, however creating a dominant language that slowly increases in popularity under a one-world government (also see this question) is extremely possible, even probable.

How you go about creating this government and keeping it in power long enough to effect language is your choice, although the linked questions should give you a few ideas.