def METHOD_NAME(self):
    addon = addon_factory(summary='Foo', description='Bar', default_locale='de')
    custom_desc_en = (
        # this is predefined in strings.jinja2 (and localized already)
        'Block invisible trackers and spying ads that follow you around the web.'
    )
    custom_desc_fr = (
        'Bloquez les traqueurs invisibles et les publicités espionnes qui vous '
        'suivent sur le Web.'
    )
    custom_desc_de = (
        'Blockieren Sie unsichtbare Verfolger und Werbung, die Sie beobachtet '
        'und im Netz verfolgt.'
    )
    item = DiscoveryItem.objects.create(
        addon=addon, custom_description=custom_desc_en
    )
    # we have l10n for fr
    with self.activate('fr'):
        item.reload()
        assert self.serialize(item, 'fr')['description_text'] == {
            'fr': custom_desc_fr,
        }
        with override_settings(DRF_API_GATES={'v5': ('l10n_flat_input_output',)}):
            assert self.serialize(item, 'fr')['description_text'] == custom_desc_fr
    # but we don't for az
    with self.activate('az'):
        item.reload()
        assert self.serialize(item, 'az')['description_text'] == {
            'de': custom_desc_de,
            'az': None,
            '_default': 'de',
        }
        with override_settings(DRF_API_GATES={'v5': ('l10n_flat_input_output',)}):
            assert self.serialize(item, 'az')['description_text'] == custom_desc_de
        # cover the edge case where the addon is set a default locale we don't have
        item.addon.update(default_locale='az')
        assert self.serialize(item, 'az')['description_text'] == {
            'en-US': custom_desc_en,
            'az': None,
            '_default': 'en-US',
        }
        with override_settings(DRF_API_GATES={'v5': ('l10n_flat_input_output',)}):
            assert self.serialize(item, 'az')['description_text'] == custom_desc_en