Dalek was the language of the Daleks and used for their writing. (PROSE: Twice Upon a Time) "The Time War" translated into Dalek was "Pa-Jass Vortan". (PROSE: The Slyther of Shoreditch)
The Dalek word for sewer was the same as the word for graveyard. (TV: The Witch's Familiar) Swearwords also existed in Dalek. When reading text about the Professor Helen Clay from the Pathweb, the Twelfth Doctor noticed and ignored swearwords about what the Daleks viewed to be inferior species. (PROSE: Twice Upon a Time)