The XSL stylesheets currently process the lang attribute
without normalising its value. Only the forms ll (language
code only) or ll_ll (language plus underscore plus
lowercase country code) are allowed. Since actually ISO-
3166 should dictate the format, the correct form ll-UU (using
an hyphen and uppercase country codes) is not working.
Normalisation of the values to some format (probably the
current one) is advisable to restore conformance and
maintain backward compatibility without disrupting the
hyphenation files naming convention (upper/lowercase
names are dangerous in multiplatform projects).