General inability:
* Illiterate: This means someone cannot read or write at all.
* Unable to decipher: This implies difficulty understanding the writing due to its complexity or illegibility.
* Unable to comprehend: This suggests you can read the words but don't understand their meaning.
* Cannot make out: This is similar to "unable to decipher," emphasizing the difficulty in recognizing the written characters.
Specific to the situation:
* Can't read the handwriting: This highlights the specific problem with the handwriting being unclear.
* Don't know the language: This points out the barrier of the language being unfamiliar.
* Not familiar with the font: This indicates difficulty recognizing the specific typeface used.
* Can't see it clearly: This acknowledges a visual impairment that prevents reading.
Informal expressions:
* Can't make head or tail of it: This emphasizes the complete lack of understanding.
* Looks like hieroglyphics to me: This uses humor to express confusion.
* It's Greek to me: This idiom means something is completely unintelligible.
Choosing the best word depends on the specific situation and the level of formality desired.