FcLangSetAdd − add a language to a langset
#include <fontconfig/fontconfig.h>
FcBool FcLangSetAdd (FcLangSet *ls, const FcChar8 *lang);
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.