#include <fontconfig.h>
FcBool FcLangSetAdd(FcLangSet *ls, const FcChar8 *lang);
FcBool FcLangSetAdd
lang is added to ls. lang should be of the form Ll-Tt where Ll is a two or three letter language from ISO 639 and Tt is a territory from ISO 3166.
Fontconfig version 2.8.0