Rename locale tags to comply with rfc5646
- From rfc5646 (section 2.1): A language tag is composed from a sequence
of one or more "subtags", each of which refines or narrows the range
of language identified by the overall tag. Subtags, in turn, are a
sequence of alphanumeric characters (letters and digits),
distinguished and separated from other subtags in a tag by a hyphen
("-", [Unicode] U+002D).
- Update Makefile to fix <html lang=""> definition in locale-specific
html files. Previously, locale-specific files were all produced with
lang="en", even though the content of the file was not in that
language. This update changes the Makefile to set the language value
that corresponds the locale-specific html file.