Ability to add custom "language item" in Translations

[#1]

For custom form validation and back-end integrations you will often raise an error message indicating something isn't correct. It would be great if you could define in the translations control custom language items and define the language specific warning/error (the "+" button doesn't appear to give this to you, or in fact do much). Then having the ability to access that custom language items translation from either the server or client side scripts based on the requesting users culture would complete this.