What is the oldest language that is still around?
That's a difficult question to answer for two reasons.
REASON 1. How do you define a language? Every language changes over time, so at what point do you say it's a new language and not the original one? For example, there has been a 3,000-year continuum in the evolution of Greek. There was never a decade or a century in which the younger people said, "We can't understand the language of the older people." Yet the people who live in Greece today can't understand the language of Plato. (Perhaps that's a bad example. I recently learned from a Greek lady that all university courses in Greece are taught in Ancient Greek, so anyone with a university degree actually can read Plato in the original. What a country!) The same is true of the continuity from Classical Latin through Vulgar Latin to Medieval Italian to Modern Italian. The same is true of the continuity from Sanskrit to Hindi or any of the Indic languages. From Old Slavonic to Russian, Czech or Serbian.
We have the same problem with geographical separation that we do with temporal separation. People who speak Dutch and people who speak German can't understand each other. Yet there is a rich spectrum of dialects of both languages, and where they meet, the speakers of Dutch-like German can understand the speakers of German-like Dutch pretty easily.
REASON 2. We only have detailed records of languages since the technology of writing was invented, and only in places where it was used. It's a common phenomenon that languages with small communities of speakers change more slowly than those with a more cosmopolitan community; this makes sense because the fewer the people, the fewer the influences for change. But the languages with the smallest number of speakers are the ones that have never been written down, or at least not until modern times. So we have difficulty knowing how much they've changed over the centuries.
Of course using anthropology and comparative linguistics as forensic tools, we can identify related languages and the migration routes of their people, and make very good guesses as to how long ago the common ancestor existed from which they both diverged, but it's hard to say anything about the speed of that divergence.
If there's a language whose speakers three thousand years ago could understand their modern descendants, it's a good bet that it's the language of a small tribe that's still living in the Stone Age, in the Amazon, New Guinea, Australia, or the African outback. But that's a "good bet," not a "sure thing."
If I had to come up with an answer to the question in the O.P. in the spirit of good scientific fun, I'd suggest Icelandic. Comparative linguistics says it's still very similar to the Old Norse that was the ancestor of all the Scandinavian languages, and it's not inconceivable that a modern Icelander could converse with an ancient Norseman. This would make it somewhere between 1500 and 2000 years old.
But someone who voted for an Australian or Amazonian language is probably more correct, he just has no way of proving it.
According to a book called Your Mother's Tongue by Stephen Burgen, the words 'shit' 'fart' and 'arse' have been around since the 10th century.
They go back much further than that, so this guy's scholarship is questionable. "Shit" occurs in all the Germanic languages:
Scheiß in German,
skid in Danish. This means it's at least 2500 years old, going back to the split among the Northern, Eastern and Western Germanic groups of languages. "Fart" and "arse" occur in German as
Fürz and
Arse, so they go back at least to the 5th century CE when the Angles, Saxons and Jutes sailed to Britannia and brought Old German with them. They may also exist in the Scandinavian languages and be much older; I'm not an expert in profanity.
what if...Antarctica has some hidden civilization deep underneath its ice...imagine us decoding those texts
Civilization, literally "the building of cities," is a technology. Like all technologies it is a virtual commodity consisting almost entirely of knowledge, so it spreads rapidly. The practices and artifacts of cities radiate outward from them at a fairly rapid clip. For example, there was a Bronze Age in northwestern Europe, even extending across the Channel into the British Isles, several centuries before the Romans built cities in those places, and in fact it appears to have sprung up before Roman civilization itself, having spread out from Greece and the Etruscans or perhaps just from trade with the Phoenicians.
It is inconceivable that a civilization could have existed and vanished without leaving traces of its influence among the people for hundreds of miles in every direction. Even if its demise led to the eventual reversion of the satellite cultures to a purely Neolithic lifestyle, its broken and discarded durable artifacts would be scattered through every archeological dig within a broad radius.
The Navajo take great pride in eschewing the White Man's ways and living by their traditions, and they keep a good buffer between their settlements and the nearest American towns in Arizona, New Mexico, Colorado and Utah. But take a drive through the Navajo nation, on its paved roads. Watch the truck traffic and count the TV antennas.
Throughout history many Neolithic peoples have joyfully embraced the promise of civilization, even if that promise turned out to be an illusion. The archeological sites of their ancient villages are giant trash dumps of artifacts bartered from the city or built with technology copied from the city.
If there is a lost civilization on Antarctica, there will be traces of its remains in Tierra del Fuego, New Zealand, the tip of Africa, etc.