Thnx for your reply,
the error was all bangla characters were showing ‘??????’ whenever I finished writing in Bangla. I have managed to resolve this problem. By commenting out //DB-Charset & //Db-Collate in wp-config.php file. Now its working fine.
Recently I have installed wordpress Multisite in one of my site. Its a fresh copy of wordpress and a fresh new Database. But the solution isn’t working for my multisite.
Is there a problem in multisite? or multisite simply do not support bangla language?