中文對文章「太難看不懂」、講話「含糊聽不懂」和寫得「太草看不懂」的「不懂」共用一詞，沒有區分。但英文前兩者「文章看不懂」、「講話聽不懂」是 unintelligible/not intelligible, 「字看不懂」卻是 illegible/not legible。
illegible: (of writing or print) impossible to read because of being very untidy
“his handwriting is totally illegible” 他的字完全看不懂
以下是 Collins English Dictionary 對 unintelligible 的解釋：
Unintelligible language is impossible to understand, for example because it is not written or pronounced clearly, or because its meaning is confused or complicated.
“He muttered something unintelligible.”
台灣學校裡大概都會教 intelligible, unintelligible, not intelligible，但 legible, illegible, not legible 幾乎都沒教，因此一般人在表達「他的字完全看不懂」時，往往都會說成 *“his handwriting is totally unintelligible”。(Jerome Su, 12/31/19)