Sometimes translation overrides become invalid. Usually it’s because of missing interpolation keys. There are two reasons for that:
The override was created before we added checks for those keys.
We update a translation and add or remove an interpolation key.
It would be great if Discourse could notify admins about such problems. Either on the dashboard or via PM.
This feature shouldn’t be too hard, since the checks are already implemented in discourse/locale_file_checker.rb at master · discourse/discourse · GitHub