There are two ways of doing this.
The first one is having the model output various languages directly. This works decently, but the traditional NLP pipeline this game uses for various critical things requires everything to be in English. Rewriting it would not only be a monumental effort for each supported language, but it would also require me to have a native speaker level understanding of each language's grammar.
The second one is simply translating the player's input to English, proceeding as normal, then translating the model's output to the player's language using the model itself. This works decently, but it means the model has a context window of the one message it translates, which leads to a very inconsistent experience, and also requires two additional API calls, making it very slow. It's feasible, but I wasn't happy with it the last time I tried it.