Characteristica universalis is the name of Gottfried Wilhelm Leibniz's project to design a philosophical language, more specifically, an arithmographic language. The language has never been published; it is unknown whether Leibniz ever worked it out in detail.
The ideal of a universal philosophical was not an idea original to Leibniz- he was preceeded by Dalgarno and Wilkins. Leibniz differed from them both in his ambition and methodology. He was more ambitious (first of all) in that he wanted his language to enable, through calculation and proper understanding of the facts, the solution to any problem.
His metholology involved comparative analysis of languages to construct his. Inspired by Chinese he removed gender, number, case, mood and personal flexion to create a highly isolating language. Adverbs and adjectives were made indistinguishable, and adjectives/adverbs and nouns were given tense.