      app_configs = apps.get_app_configs()
      allowable_packages = set(app_config.name for app_config in app_configs)
      allowable_packages.update(DEFAULT_PACKAGES)
      packages = [p for p in packages if p in allowable_packages]
      t = {}
      paths = []
      en_selected = locale.startswith('en')
      en_catalog_missing = True
      # paths of requested packages
      for package in packages:
 
</s> remove     en_selected = locale.startswith('en')
    en_catalog_missing = True
 </s> add  </s> remove     default_locale = to_locale(settings.LANGUAGE_CODE)
 </s> add  </s> remove     # add the filesystem paths listed in the LOCALE_PATHS setting
    paths.extend(reversed(settings.LOCALE_PATHS))
    # first load all english languages files for defaults
    for path in paths:
        try:
            catalog = gettext_module.translation(domain, path, ['en'])
            t.update(catalog._catalog)
        except IOError:
            pass
        else:
            # 'en' is the selected language and at least one of the packages
            # listed in `packages` has an 'en' catalog
            if en_selected:
                en_catalog_missing = False
    # next load the settings.LANGUAGE_CODE translations if it isn't english
    if default_locale != 'en':
        for path in paths:
            try:
                catalog = gettext_module.translation(domain, path, [default_locale])
            except IOError:
                catalog = None
            if catalog is not None:
                t.update(catalog._catalog)
    # last load the currently selected language, if it isn't identical to the default.
    if locale != default_locale:
        # If the currently selected language is English but it doesn't have a
        # translation catalog (presumably due to being the language translated
        # from) then a wrong language catalog might have been loaded in the
        # previous step. It needs to be discarded.
        if en_selected and en_catalog_missing:
            t = {}
        else:
            locale_t = {}
            for path in paths:
                try:
                    catalog = gettext_module.translation(domain, path, [locale])
                except IOError:
                    catalog = None
                if catalog is not None:
                    locale_t.update(catalog._catalog)
            if locale_t:
                t = locale_t
 </s> add     trans = DjangoTranslation(locale, domain=domain, localedirs=paths)
    trans_cat = trans._catalog
 </s> remove     for k, v in t.items():
        if k == '':
 </s> add     trans_fallback_cat = trans._fallback._catalog if trans._fallback else {}
    for key, value in itertools.chain(six.iteritems(trans_cat), six.iteritems(trans_fallback_cat)):
        if key == '' or key in catalog: </s> remove     if '' in t:
        for l in t[''].split('\n'):
            if l.startswith('Plural-Forms:'):
                plural = l.split(':', 1)[1].strip()
 </s> add     if '' in trans_cat:
        for line in trans_cat[''].split('\n'):
            if line.startswith('Plural-Forms:'):
                plural = line.split(':', 1)[1].strip()
      app_configs = apps.get_app_configs()
      allowable_packages = set(app_config.name for app_config in app_configs)
      allowable_packages.update(DEFAULT_PACKAGES)
      packages = [p for p in packages if p in allowable_packages]

      paths = []
      en_selected = locale.startswith('en')
      en_catalog_missing = True
      # paths of requested packages
      for package in packages:
keep keep keep keep replace keep keep keep keep keep
 Reused the DjangoTranslation class for the javascript_catalog view

Thanks Tim Graham and Cristiano Coelho for the reviews.
Refs #26328, #26319. 
django/views/i18n.py