All files called Rules-* in the po/ directory get appended to the po/Makefile when it is created. They present an opportunity to add rules for special PO files to the Makefile, without needing to mess with po/Makefile.in.in.
GNU gettext comes with a Rules-quot file, containing rules for
building catalogs email@example.com and firstname.lastname@example.org. The
effect of email@example.com is that people who set their
environment variable to ‘en@quot’ will get messages with proper
looking symmetric Unicode quotation marks instead of abusing the ASCII
grave accent and the ASCII apostrophe for indicating quotations. To
enable this catalog, simply add
en@quot to the po/LINGUAS
file. The effect of firstname.lastname@example.org is that people who set
LANGUAGE to ‘en@boldquot’ will get not only proper quotation
marks, but also the quoted text will be shown in a bold font on terminals
and consoles. This catalog is useful only for command-line programs, not
GUI programs. To enable it, similarly add
en@boldquot to the
Similarly, you can create rules for building message catalogs for the sr@latin locale – Serbian written with the Latin alphabet – from those for the sr locale – Serbian written with Cyrillic letters. See msgfilter Invocation.