Ruathlek

Ruathlek was the "secret language" or magical script of illusionists. Waterdeep was known to hold at least one library of books in this dweomer-guarded tongue.

History
Ruathlek was descended from the Netherese language. It was said that Leira, the goddess of illusion and deception, developed Ruathlek with some of the descendants of Netheril, the wizards of Nimbral. Unlike most illusionists, the people of Nimbral used Ruathlek as both a magical script and their mundane, everyday language.