How to override a system message for duplicates in register page

Hello everybody

I want to override the prevent duplicate values in the field username, recently I changed the authentication from username to email, now everybody will authenticate with their email, everything is working fine.

In the register page now is asking for email instead of flat username, but when a user try to register and use the existent email, the validation shows the messageUsername Email@anyemail.com already exists. Choose another username.

I customize the message in the field properties on the email field and I ticked Prevent duplicate values and I added a message "E-mail %value% already exists, use anothere-mail address."

and doesn't fire that message, always shows the system message "Username Email@anyemail.com already exists. Choose another username"

How can I override that message?

Maybe it's a bug.
Please don't tell me to modify the languages files (*.lng) in "C:\Program Files\PHPRunner10.4\lang"