Hi
To translate this system string, please translate the below file
/root/resources/lang/en/validation.php
by following below rules
You have to keep :attribute
text untranslated, it will be change by your input name, and translate all others. Example
'accepted' => 'The :attribute must be accepted.',
Will be translated to spanish
'accepted' => 'El :attribute debe ser aceptado.',
Hope it will help you
Best regards