Improved and fixed grammar mistakes. Added pluralized messages
minor #9765 [Validator] Improved and fixed grammar mistakes. Added pluralized messages (benatespina)

This PR was submitted for the 2.3-dev branch but it was merged into the 2.3 branch instead (closes #9765).

Discussion
----------

[Validator] Improved and fixed grammar mistakes. Added pluralized messages

| Q                  | A
| ------------------- | ---
| Bug fix?	      |no
| New feature?	|no
| BC breaks?	|no
| Deprecations?	|no
| Tests pass?	|yes
| Fixed tickets
| License	|MIT
| Doc PR

Commits
-------

d38dbd5 [Validator] Improved and fixed grammar mistakes. Added pluralized messages