Support character-wise line break in `insert_textbox` for CJK

[JorjMcKie]

Discussed in #4972

^{Originally posted by yinghao-xue April 22, 2026}
When using Page.insert_textbox()to insert mixed Chinese and English text

“Van Dyke等人进行的一项回顾性病例系列研究强调了三份独立病例中Elevess引起的严重急性局部反应和结节性无菌性脓肿的形成。”

the automatic line-breaking logic treats English as words and CJK as characters. This causes premature line breaks after English words. It looks like this:

Van Dyke
等人进行的一项回顾性病例系列研究强调了三份独立病
例中 Elevess
引起的严重急性局部反应和结节性无菌性脓肿的形成。

we tried add or remove space between Chinese and English characters, but none looks normal. How can we achieve proper line breaking?

[JorjMcKie]

This can be restricted to Unicode CJK_RANGE = range(0x4E00, 0xA000) which covers Chinese and Japanese. The implementation must also take care of Unicode mixtures inside / outside CJK_RANGE.