Daily.co has expanded its API language support to include Dutch, English, Finnish, French, German, and Portuguese, allowing users to set the language preference using various methods including the front-end or REST APIs, domain-level setting, room-level setting, token-based setting, and user's browser settings. The language priority order is setDailyLang(), token, DailyIframe property, room, and domain. Users can also contribute to translating new languages by contacting Daily.co.