Bad news: there's a bug in asdf 2.20,
such that I recommend you use either 2.019.8 (2.20 minus the bug)
or 2.20.7 (that I hope to promote to 2.21 at the end of the month).
Bug report: in contrib/encodings/generate.lisp, you erroneously define
latin5, latin6, etc., as respective aliases for iso-8859-5, iso-8859-6, etc.