Problem:
I have a form to create a relationship between a Coach and a Trainee. If the user types into the select2 field(for either parent or child) a name that is already connected, the error message reads "No coach can be associated to [NAME]" or "No trainee can be associated to [NAME]"

This is terrible English and I want to be able to craft a better error message for the user. This message is not available in the Messages pane of the relationship form page. Where can I edit this text?

I also want to edit the placeholder text in the select2 (it current says "Search for a post")
Solution:

Relevant Documentation:
Another option: https://toolset.com/forums/topic/how-do-i-change-the-error-text-associated-with-select2-in-a-relationship-form/#post-2603489