If you like you Windows 7 in Bangla (or Bengali) the official language of Bangladesh, then download the latest Windows 7 Language Interface Pack (LIP) now.
Download the Bangla Windows 7 LIP via the Microsoft.com Download Center.
Please note that the Bangla Windows 7 LIP can only be installed on a system that runs a English client version of Windows 7. It is available for both 32-bit and 64-bit systems on the Download Center.
You can download the Windows Vista Bangla LIP (and many others for both Windows 7 and Windows Vista) and it is also available for Windows XP