[Minor BC] Remove translation of validator keys

Removes the translation of validator message ***keys*** which is totally
absurd in the first place. They are constants that should not be
modified.
Merge pull request #5664 from macnibblet/hotfix/remove-validator-message-key-translation

[Minor BC] Remove translation of validator keys
[#5664] Added note to README

- Like #5666, this is technically a BC break and needs a note in the changelog.
Merge branch 'hotfix/5664' into develop

Close #5664