I was curious about why Cantonese is Hong Kong's official language. Here are some excerpts from Wikipedia:
"After the British acquired Hong Kong Island, Kowloon Peninsula and the New Territories from the Qing in 1841 (officially 1842) and 1898, large numbers[quantify] of merchants and workers came to Hong Kong from the city of Canton, the main centre of Cantonese. Cantonese became the dominant spoken language in Hong Kong.
In 1949, the year that the People's Republic of China was established, Hong Kong saw a large influx of refugees from mainland China, prompting the Hong Kong Government to close its border.[citation needed] Illegal immigration from mainland China into Hong Kong nevertheless continued.
Movement, communication and relations between Hong Kong and mainland China became very limited, and consequently the evolution of Cantonese in Hong Kong diverged from that of Guangzhou. In mainland China, the use of Mandarin as the official language and in education was enforced. In Hong Kong, Cantonese is the medium of instruction in schools, along with written English and written Chinese."
https://en.wikipedia.org/wiki/Hong_Kong_Cantonese#:~:text=After%20the%20British%20acquired%20Hong,language%20in%20Hong%20Kong.%20The