Change the default "this field is required"

From this page https://gist.github.com/BronsonQuick/2366001
I tried applying this, but it doesn't work.
Please advice. Thanks

//This is a filter to change the default validation message that Gravity Forms generates
add_filter('gform_validation_message', 'change_validation_message', 10, 2);
function change_validation_message($message, $form)
{
return "<div class='validation_error'>Oops! Looks like there’s something wrong. Please review the form above.</div>";
}

I would also be interested in a hook to change that default required message for fields.

Seems the code you used above @siwbao targets the main error, no the field errors.

Cheers.