Complex sentence: The vernacular language spoken in the city is Shanghainese, a dialect of the Taihu Wu subgroup of the Wu Chinese family, while the official language nationwide is Standard Mandarin, itself completely mutually unintelligible with Wu Chinese.
Split into simpler sentences: The vernacular language spoken in the city is Shanghainese, a dialect of the Taihu Wu subgroup of the Wu Chinese family. This makes it a different language from the official language nationwide, which is Mandarin, itself completely mutually unintelligible with Wu Chinese.