I’ve just submitted the pointless-size package.
Now you can use Chinese size system (字号/号数制) as the following:
#import "@preview/pointless-size:0.1.0": zh, zihao
#set text(size: zh(5)) // 五号（10.5pt）
// or
#set text(zh(5))
#show: zihao(5)
// 小号用负数表示 use negative numbers for small sizes
#zh(-4) // 小四（12pt）
#zh(1) // 一号（26pt）
#zh(-1) // 小一（24pt）
#zh("-0") // 小初（36pt）
#zh(0) // 初号（42pt）
The special size system in Chinese and Japanese Typesetting is called 号数制 (hào-system, or number system), and it is still commonly used in China. The unit is not linearly related to points: 五号 (size 5) = 10.5pt, 小四 (size small 4) = 12pt, 四号 (size 4) = 14pt, … Therefore, people always have to search for a conversion table when #set text(size: …) without this package.
// The hào-system was developed during the modernization of China, since the Qing dynasty (清朝). As a result, it has a complicated history and is never standardized… I put some links on it in the README: