The mini expansion contains 8 new province tiles "Mango village" you can build by using two of a kind (color doesn't matter) and the normal building action.
They give small bonuses when being placed like river movement, karma, new dice, upgrade, money. In addition they contain new spots for your workers to score any two of your mango villages again (scaled like the markets for player number).
Finally there is a new brown yield tile for the Navaratnas variant which gives you 3$ for each mango village in your province.
You can't overbuild Mango villages via Master Builder, but you can use Master Builder with the normal 5 and another 5 to build the Mango village over other province tiles.
Rules are in English and German but tiles are language neutral.