You can create a new file in your resources/lang/vendor/backpack/en/base.php
. Any language strings that are there will be preferred, over the ones in the package.
Alternatively, you can use
php artisan vendor:publish --provider="Backpack\CRUD\BackpackServiceProvider" --tag="lang"
which will publish ALL lang files, for ALL languages, inside resources/lang/vendor/backpack
. But it's highly unlikely you need to modify all of them. In case you do publish all languages, just delete the ones you didn't overwrite. That way you only keep what's custom in your custom files, and it'll be easier to upgrade those files in the future.