The language used in online forums of Hong Kong is highly colloquial and provides an authentic representation of language use among Hong Kong netizens. Meanwhile, the theoretical perspective of translanguaging offers valuable insights into their multilingual lives, enabling an effective exploration and in-depth analysis of the construction of Hong Kong netizens’ cultural identity. Through classification and analysis of the language use in Hong Kong online forums, this study identifies the following characteristics of Hong Kong netizens’ translanguaging practices: (1) multicode integration, as reflected in Cantonese–English mixing, multilingual borrowing, and the use of mixed semiotic resources; (2) diverse linguistic innovation, manifested in the creation of new words through transliteration and homophony, compound formation, functional shifts of word classes, and new interpretations of existing words; (3) strong community specificity in online buzzwords. Based on these, the cultural identity of Hong Kong netizens can be characterised by hybridity, local subjectivity, fluidity, and innovative selective appropriation. In particular, its fluidity reflects their construction of national identification after Hong Kong’s return and deepening recognition of their identity as Chinese, national development and the integrated development of the Guangdong-Hong Kong-Macao Greater Bay Area. Translanguaging serves as symbolic representations through which Hong Kongers actively construct their cultural identity. In turn, it also reinforces Hong Kongers’ awareness of identity boundaries, sense of cultural belonging, emotional attachment, and capacity for continuous innovation. Such translanguaging practices concretise Hong Kong’s cultural diversity through language, while demonstrating the resilience and creativity embedded in Hong Kong culture.