We make contact with an alien civilization. Our sensors detect they'll arrive at earth in just a few hours time, but they send us an advance message. Our scientists receive it but nobody understands, it's an audio recording in some kind of strange language. Sure enough, a lone translator finally decodes it with minutes to spare and delivers the message to the President.
"Thousands of years ago our ancestors crash-landed on your planet. They managed to send off a distress signal before they lost all power and once we heard we set a course for your planet at maximum speed, although we predict nearly 10,000 of your solar cycles have gone by since the distress signal was sent. Anyway, we've scanned your planet for traces of our ancestors but find only faint signal, as if they've been stamped out. What happened to them? We require answers."
The President and his cabinet scratch their heads for a bit, confused. Finally the President turns to the translator and asks: "How did you decode this message so fast?"
"Oh, it was simple", says the translator. "Turns out they speak Cherokee."
A friend of mine wrote this little gem: