Using GNU Guix, I had to replace the declare-default language line of the testsuite/expr-lang.dsl from:
(declare-default-language (language "EN" "US"))
to
(declare-default-language (language "EN" "US.UTF-8"))
Otherwise, it would fail like this:
../jade/openjade -c ../dsssl/catalog -t sgml -d expr-lang.dsl null.sgml > expr-lang.actual
lt-openjade:expr-lang.dsl:119:1:E: "#f" not a language as required in a default-language-declaration
lt-openjade:E: no current language