Historians and sociologists have done research. The Three Kingdoms belong to the late Han Dynasty, that is, the late Eastern Han Dynasty. The founder of the Han Dynasty was Liu Bang. Liu Bang was born in Xuzhou City, Jiangsu Province. Most of his ministers and generals came from Jiangsu, such as Xiao He (Fengxian County, Jiangsu Province), Han Xin (Huaiyin County, Jiangsu Province), Fan Kuai (Peixian County, Jiangsu Province) and Zhou Bo (Fengxian County, Jiangsu Province).
The official language of a dynasty mainly depends on the dialect of the royal family, so the political power established by these people basically uses Wu as the official language.
Therefore, in the late Han and Three Kingdoms period, the official language of North Korea should also be Wu.
After the establishment of the Three Kingdoms, Cao Shi's family has always been a big official of the Han Dynasty, so most of the official language is Wu, so after Cao Pi established Wei, the official language should also be Wu; Sun Quan of Dongwu is from Hangzhou, Zhejiang Province, so the official language of Wu is Wu dialect. Liu Bei was born in Zhuozhou, Hebei, and Zhuge Liang was born in Linyi, Shandong. Neither of them really held an important position in the Han Dynasty, nor were they born in Jiangsu, Zhejiang and Shanghai. Therefore, it is very likely that the official dialect of Shu is not Wu dialect, and the specific dialect is not clear for the time being.