If global communication comparable to the Internet had existed from the beginning of time, would humans still have developed thousands of languages?
The other day I was considering an alien species that had somehow evolved to use shortwave radio as its natural form of communication. Shortwave radio signals can reflect off the ionosphere (called skywave or skip propogation) to reach listeners well beyond the horizon (as much as 3500 km on Earth). It occurred to me this species would be "connected" before mastering agriculture, animal husbandry, perhaps even cave painting.
But would that prevent them from developing distinct languages? Probably not. As useful as it can be to speak to someone halfway around the world, local communication is far important for your survival (think: signage, directions, medical treatment, civil service interactions, education...). That person you're speaking with on the other side of the world probably isn't fluent in your language just because they can connect to people far away but because it's locally useful. There will always be a local influence shaping language in ways foreign influence can't compete with. Look at the loanwords English has slowly (but not universally) incorporated over the centuries as English speakers encountered new people, new animals, new customs and styles and such.
So languages would still evolve, still require translation and education, and still compete for regional (and global) dominance, but it would likely all play out in a shorter period than it has on Earth because it will never be subject to the delaying effect of pre-industrial transportation.
If the moment a good idea or new concept was developed it could be immediately shared everywhere then new words, ideas, inventions, and phrases would spread virally. Just look at how the internet has changed our language and culture in such a short time. New slang and phrases pop up and disappear overnight. When was the last time you saw somebody un-ironically type in the "LULZ ROFL LMAO XD LE EPIC TACO SPORK RANDUMB HUMOR!" style of expression that was typical to the myspace era of web history? It was only a few years years ago really, but its already an antiquated vernacular and it only existed for a few years to begin with. Prior to telecommunications words and sayings lasted centuries, remained fairly localized, and referred to very specific cultural phenomenon, now they last maybe a few months and you will find kids from Nigeria online using words like "Thot." "bae" or "fuk-boi"only a few weeks after they pop into popular use. If anything telecommunication vastly accelerates linguistic development.