🌐(i18n) add spanish and chinese (#884)

All the spanish and chinese translations are complete on crowdin. We
activate it in django settings and download all translations from
crowdin

Signed-off-by: virgile-deville <virgile.deville@beta.gouv.fr>

src/backend/impress/settings.py

@@ -239,6 +239,8 @@ class Base(Configuration):
             ("fr-fr", "Français"),
             ("de-de", "Deutsch"),
             ("nl-nl", "Nederlands"),
+            ("es-es", "Spanish"),
+            ("cn-cn", "Chinese"),
         )
     )