Here Gee seems to be talking about traditional PC games where the internal design of a game is determined by the game designers. But MMOGs is a different story. The internal design of MMOGs is decided by both game designers and game players. Game designers set up the basic narratives, basic functions, and basic rules of playing. But since players are allowed to communicate with each other in the game, and forced to play together when they reach a certain level, they construct part of the internal design of the game, such as the way to make friends in the game, the way to make/join a team in the game, the way to follow and learn from players with more expertise, etc. In some games, the two parts of internal design actually communicate with each other. That is, the game designers adapt the game to the expectations and practice of majority players.
Since MMOGs are partly designed by the game players, it's interesting to consider what may happen when L2 learners play a MMOG that is produced and largely played in the target society. On one hand, we may ask what they need to know in order to play the game well? Well, first of all they need to know the internal design of the game that is decided by the game designers, like how to gain credits and where the game narrative leads to. Also, they need to know the internal design of the game that is decided by the game players, mainly native speakers of the target language.
On the other hand, it's inevitable that L2 learners will bring in their own culture/practice when they play. Because the internal design of a MMOG is partly decided by the players, how might L2 learners change the internal design of the game?
