I have always heard that mutual intelligibility between the Sinitic languages of China is low. However, I am confused by the sociolinguistics of Hong Kong cinema in 1980s and 1990s. Films from that period often contain extensive dialogue in pure Mandarian (as when a character is from the mainland or Taiwan) or Shanghai dialect (in films depicting the many Shanghainese emigrants to HK).

Were Hong Kong audiences expected to be able to follow this dialogue without assistance? Or were subtitles necessary when these films were first screened in Hong Kong cinemas? And how realistic is the trope that a visiting Taiwanese person, who speaks Mandarin, could easily understand the Cantonese speakers around him?