Text and HTML assets support localization. Full details can be found in the RPI Reference guide.
When using localized content in a Realtime context, the following Realtime app setting allows for specification of the visitor profile parameter that will be used to persist a region/language code value:
RealtimeAPIConfiguration__AppSettings__RegionLanguageCodeParameter
If this is not set, RPI will attempt to use the standard region/language code captured by a page visit ('en-US').