Added functions

【Contents of modification】
■New function “Link Menu (for switching foreign language sites)” added.
・This is a function to add a link with an icon next to the global menu. This is suitable for displaying links with country flag icons when you have created a site in another language.

The following are the files that have been modified for this update.
【Corrected files】.
admin/inc/basic.php
admin/js/my_script.js
admin/theme-options.php
functions/head.php
js/jscript.js
languages/ja.mo
languages/ja.po
header.php
style.css