Take an AAA game, and look at the generic. You'll see in what languages the game have been translated ; generally less than a dozen and it's globally the same language whatever the game.
It's not cheap to translate a game, therefore they target the biggest markets, to be sure that it will increase their sell, and not just their cost. And it don't change much that you are making an adult game. Globally speaking, you don't come to adult video games if you don't already play video games. Therefore, the languages with the highest number of people playing "regular games" will also be the languages with the highest number of people playing adult games.