The Daleks had a form of writing.
Dalek text was written in the Dalek language. (PROSE: Twice Upon a Time)
During the 22nd century invasion of Earth, the Daleks placed notices around London locations with uncertain meaning. (TV: The Dalek Invasion of Earth)
Dalek writing was displayed both on screens and in the vision of certain Dalek factions. (TV: Remembrance of the Daleks)
Daleks that originated from the Last Great Time War possessed markings below their eyepieces for identification. (TV: Dalek, The Parting of the Ways, Doomsday, Daleks in Manhattan, Evolution of the Daleks, The Stolen Earth, Journey's End)
The War Doctor could understand Dalek writing, to a degree at least, and was skilled at hacking into the Daleks' databanks. (PROSE: Engines of War) After Rusty projected information about Professor Helen Clay from the Pathweb, the Twelfth Doctor read the text, which was written in Dalek, though he ignored the swearwords describing what the Daleks saw as inferior life forms. (PROSE: Twice Upon a Time)