The bot speaks every language the community has translated it into, and most languages come in several versions: plain, safe for work, or themed after a film, a game or a series, where the villagers and wolves become something else entirely. The community page lists them all.
For your group
/config → Language changes the language of the games in the group. Pick the language, then the version.
For yourself
/setlang changes the language of the bot's private messages to you.
Help translate
Every language file is written by players. To fix a translation, or to start a new language or a themed version, ask in the support group and we will put you in touch with the translators. New and changed files are checked before they go live.