Fixed on translation file loading/updated page builder

【Contents of correction】
■Fixes related to translation file loading
■Page builder update (for WordPress 5.5)

The following files have been modified for this update.
【Fixed files】
functions.php
functions/update_notifier.php
languages/ja.mo
languages/ja.po
pagebuilder/assets/admin/css/admin.css
pagebuilder/assets/admin/js/admin.js
pagebuilder/assets/admin/js/editor.js
pagebuilder/assets/admin/js/repeater.js
pagebuilder/assets/admin/js/slider.js
pagebuilder/assets/css/slider.css
pagebuilder/modules/googlemap.php
pagebuilder/modules/simple_table.php
pagebuilder/modules/slider.php
pagebuilder/modules/tab.php
pagebuilder/pagebuilder.php
style.css