$ rpm -qf "$(which fc-list)"
fontconfig-2.6.0-alt1

If a I pass some language as the pattern to fc-list:

$ fc-list :lang=udm; echo $?
0
$ 

and the result is empty, then two situations are indistinguishable: 

1) there are no fonts available for the Udmurt orthography;
2) the Udmurt orthography is not known to fc-list.

I suggest that

$ fc-list :lang=qwerty
$ 

should issue a warning that language "qwerty" is not known to it.