(Beta feature, not all screens are localized yet, translation is under review, we welcome your feedback about the translation quality)
You can set the default language of your microsite by going to Site Admin -> Site Details -> User Interface tab. Currently we have added French, French Canada, German, Spanish, Portuguese and Dutch besides default English. You can also enable allowing users to select their preferred language.
If the users are allowed to select language, then they would see a menu option in the header which will allow them to select their preferred language for the session.
To restrict the number of languages available to pick, add LANGUAGES property in the Site Admin->Site Details->Customization and specify languages separated by comma. For example following will enable only English and Spanish options.