'Merge the given translations into the catalog.
Message translations in the specified catalog override any messages
with the same identifier in the existing catalog.
:param translations: the `Translations` instance with the messages to
merge
:return: the `Translations` instance (``self``) so that `merge` calls
can be easily chained
:rtype: `Translations`'

def merge(self, translations):

    if isinstance(translations, gettext.GNUTranslations):
        self._catalog.update(translations._catalog)
        if isinstance(translations, Translations):
            self.files.extend(translations.files)
    return self
