Cacher is the code snippet organizer for pro developers

<?php
/**
 * Gravity Perks // GP Limit Checkboxes // Validation Messages
 * http://gravitywiz.com/documentation/gp-limit-checkboxes/
 */
add_filter( 'gplc_validation_message_field_under_min', function( $message, $form, $field_id, $group ) {
    return _n( 'You must select at least %s item.', 'You must select at least %s items.', $group['min'] );
}, 10, 4 );

// Other avialable filters:
// gplc_validation_message_field_under_min
// gplc_validation_message_field_over_max
// gplc_validation_message_group_under_min
// gplc_validation_message_group_over_max