High Nehekharan

High Nehekharan is the ancient tongue of the nobles of that dreaded land. The written form of this language is based entirely in pictograms and has no traditional alphabet, making it extremely difficult for Old Worlders to comprehend. Indeed, many necromancers do not use this difficult language, as it is possible to use Lingua Praestantia in almost all necromantic castings because of how exhaustively specific that language is. This true necromantic tongue is only used by those necromancers who have need of it for specific rituals or seek to learn the forms first set out by Nagash.

Source

 * Warhammer Fantasy RPG 2nd ED -- Night's Dark Masters (pg. 121).