How to override Entity Autocomplete required validation error message? I have entity reference autocomplete field (which is term reference field )

users are not allowed to create new terms while node creation. 



The validation error shows like below on form submit : 




  There are no entities matching "newterm".


I need to override this message with something like "No new terms are allowed please select from existing terms"

When I tried to find code from where it is working it looks from this : 

core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php and function where message is there : https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Entity%21Element%21EntityAutocomplete.php/function/EntityAutocomplete%3A%3AmatchEntityByTitle/8.0.x

Please suggest how I can override this. I tried searching lot but was not able to find right direction and have tried overriding status message as well but sure how to proceed with this. 

Thanks!
In HOOK_form_FORM_ID_alter() add #element_validate attribute to the form element

$form['field_your_field_name']['#element_validate']


Reference: https://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7.x#element_validate