Complex sentence: Most people in Sukhothai still speak the Sukhothai Dialect of Thai in their everyday lives, which has spoken in the area since the days of the Sukhothai Kingdom, some 700 years ago.
Split into simpler sentences: Most people in Sukhothai still speak the Sukhothai Dialect of Thai in their everyday lives. Which has been spoken since the formation of the Sukhothai Kingdom, some 700 years ago.