Hong Kong vs. China
"Hong Kong is not China." Technically this saying isn't either right or wrong. Hong Kong is one of a special administrative region in China, operating under the "one country, two systems" principle since July, 1997. As a foreigner, you could see "us" as one. However, as HongKongers, we see quite a lot of differences between "one country, two ethnic groups". Here could be some of the reasons why there are always conflicts between Hong Kong and China.
Traditional Chinese vs. Simplified Chinese
What is the difference between Traditional Chinese and Simplified Chinese? Traditional written Chinese characters are used in Hong Kong, while Simplified Chinese characters are a newly invention, adapted by the Chinese government about 60 years ago. Simplified Chinese was invented based on the traditional characters and reduced to fewer strokes, therefore it became a lot easier to learn and increase literacy for everyone in China.
HongKongers do not widely accept the style of Simplified Chinese because the aesthetics and the meaning behind of a Chinese character have lost when some strokes are missing. Let us explain in a common example: 愛 (T. Chinese) vs. 爱 (S. Chinese) (love, n. / v.) The character of 心 (heart, n.) is missing in the character of "love" Simplified Chinese. You can't love someone without a heart - it somehow loses its meaning while some strokes are missing.
Cantonese vs. Mandarin
Not only the written characters are different but also the spoken language are not the same between two regions. Mandarin with the Beijing dialect is the official language of China, while the official languages of Hong Kong are Chinese and English. In Hong Kong, when we say "Chinese" is literally means "Cantonese" for sure. This spoken language is rarely being used in writing unless it's conversational. Official documents are all written in formal Hong Kong style. Therefore, Mandarin speakers can usually understand the written content but not in Cantonese speaking.
Like everywhere else, we speak differently because of a different cultural background. Internet Slang can be one of the major differences in our languages. We even have different saying about the floor level - HongKongers see ground floor as ground floor while people in China believe that ground floor is the first floor.
Social Media and the Internet
Unlike people in China, HongKongers have access to the Internet and all sorts of social media platforms without the need for a VPN. Baidu (a Chinese search engine), Weibo (a social media platform) and WeChat (a communication app) are widely used in China. You are not allowed to access foreign apps and sites in China unless you have a VPN installed in your devices. Therefore, Western sites and social media platforms such as Google, Facebook, Instagram and Whatsapp are widespread in Hong Kong but not in China. WeChat is not actively used by HongKongers unless they use it for business proposes and talk to friends and family in mainland China.