Change the title of spoiler button by state

The title will give the precise representation of the current state. It
would be helpful for blind people.

app/javascript/mastodon/locales/es.json

@@ -61,7 +61,8 @@
   "compose_form.publish": "Tootear",
   "compose_form.publish_loud": "{publish}!",
   "compose_form.sensitive": "Marcar contenido como sensible",
-  "compose_form.spoiler": "Ocultar texto tras una advertencia",
+  "compose_form.spoiler.marked": "Text is hidden behind warning",
+  "compose_form.spoiler.unmarked": "Text is not hidden",
   "compose_form.spoiler_placeholder": "Advertencia de contenido",
   "confirmation_modal.cancel": "Cancelar",
   "confirmations.block.confirm": "Bloquear",