How is aZn written in Chinese?
Writing in all caps in on line chat or forums is akin to shouting in everyone's ears in real life. It is quite annoying.

Typing capital alphabets in odd positions in a word emphasize a higher volume or higher tone for its reading. For example "aZn" = aSIan and it is even more annoying than all caps.

It is considered rude, cheeky and juvenile behavior to type like that: "hEy bRO!"


  how does one render the effect of the alternating capitals and lower cases?


You can imagine using bigger font size or bolder font style for a selected few characters in an otherwise simple phrase, would create this "volume up/ raising tone" effect. 

As for using different alphabets to replace the actual one, like "prYde" instead of "Pride". You can do the same in Chinese by using a sound alike character to replace the correct one just for the fun of it.  For example:  "神馬？" instead of "什麼？"; "魂淡" instead of "混蛋" .