This is the third milestone in the "Words Collected" statistic and is obtained once you have collect 10 alien words. You can check your progress by pressing
and looking at the Milestones screen.
The easiest way to find the actual words is to visit the "Alien Artifacts" and pressing
. These artifacts are found on most worlds. With a bit of exploration I had unlocked this milestone during the tutorial at the beginning of the game before I visited the space station.
You can also learn words by speaking to aliens. Quite often they will give you an option to spend a little money and they'll teach you a word. So if you don't fancy exploring just talk to a lot of aliens.