The book, as I remember it, was pre-90's, and involved a planet or multi-planet system where they had invented three artificial languages, each of which had a different emphasis (kind of like computer languages), one good for, say, farming, one for science, one for war, etc... I don't remember the different varieties. The only other thing I remember was that they kind of all got together at the end of the book for some big sing along or something.
I bet this is The Languages of Pao (1958) by Jack Vance.
A linguist is hired to create custom languages to reform the planet of Pao.
From the summary on Wikipedia:
Somewhat later, the predatory Brumbo Clan from the planet Batmarsh raids the virtually defenseless Pao with impunity, and the Panarch Bustamonte is forced to pay heavy tribute. To rid himself of the Brumbos, he seeks the aid of Palafox, who has a plan to create warrior, technical and mercantile castes on Pao using customized languages (named Valiant, Technicant and Cogitant) and other means to shape the mindsets of each caste, isolating them from each other and the general populace of Pao. To achieve this, each caste gets a special training area where it is completely segregated from any outside influence; the necessary land is confiscated from families, some of which have held it for countless generations — which creates some disaffection in the conservative Paonese population and earns Bustamonte the name of a tyrant.