'Get a lang-specific handler for the catalog of loaded CIX files.
"lang" is the language.
"selections" (optional) is a set of catalog names (or full
path to the CIX files) to use.  Essentially it is a
filter.  If not specified, all available catalogs for
this language are used. Otherwise only the selected
catalogs are used. A catalog "name" is the
(case-normalized) basename of the .cix file.'

def get_catalog_lib(self, lang, selections=None):

    return self.get_catalogs_zone().get_lib(lang, selections)
