You can affordably master languages if you follow this technique. First, acquire around 200 Carbon. Next, find a space station. Enter the regular door and chat with the alien you find waiting there. Each brief conversation costs 20 Carbon, but every second chat will offer the chance to learn a new word. Continue talking with the alien.

Once you know enough words, other available options will appear and you can receive either an Isotope or Fuel for using them. Typically, these can be turned into 56 Carbon, a nice return on the 40 you had to spend. After a certain point, you're essentially gaining resources instead of spending them as you master the local language.