FcLangSetContains − check langset subset relation
#include <fontconfig/fontconfig.h>
FcBool FcLangSetContains (const FcLangSet *ls_a, const FcLangSet *ls_b);
FcLangSetContains returns FcTrue if ls_a contains every language in ls_b. ls_a will ’contain’ a language from ls_b if ls_a has exactly the language, or either the language or ls_a has no territory.