Show warning or error when translation key used in app_settings doesn't have translation in translation file

[1yuv]

Is your feature request related to a problem? Please describe.
Most of the SMS based projects rely on the translation key to send sms or send validaton response. However, there is no way of checking if all those translation keys put on app_settings have corresponding trasnlations put in trasnlation files or not. Missing a translation key could cause smses not to be sent and we've seen this problem already.

Describe the solution you'd like
Check and throw warning or error if translation key used in app_settings doesn't have corresponding entry in translation file(s).

[garethbowen]

Great idea. It might be useful to also check the rest of the configuration (tasks, targets, etc) for the same.