<?php

class GalleryImage extends DataExtension {
    public static $db = array(
        'Sort'  => 'Int'
    );

    public static $belogs_many_many = array(
        'Gallery'   => 'GalleryPage'
    );

    public function updateCMSFields(FieldList $fields) {
        $fields->addFieldToTab('Root.Main', TextField::create('Sort', _t('ContactPage.PRIORITY')));
    }
}

<?php

class GalleryImage extends DataExtension {
    public static $db = array(
        'Sort'  => 'Int'
    );

    public static $belogs_many_many = array(
        'Gallery'   => 'GalleryPage'
    );

    public function updateCMSFields(FieldList $fields) {
        $fields->addFieldToTab('Root.Main', TextField::create('Sort', _t('GalleryPage.PRIORITY')));
    }
}

Correct typo in priority label
Correct typo in priority label
