In spreadubuntu site, if any material is uploaded for a specific language, the flag for that language is displayed along with that material.
Such as in the following page the italian flag is displayed in the 'Language' field
http://spreadubuntu.org/en/node/568
in the following page the Russian flag is displayed in the 'Language' field
http://spreadubuntu.org/ru/material/poster/%D0%BF%D0%BE%D1%81%D1%82%D0%B5%D1%80-ubuntu-0
But there is no 'Language Flag' for the language Bengali. So if you go to the following links you'll find no flag in the 'Language' field:
http://spreadubuntu.org/en/node/536
http://spreadubuntu.org/en/node/722
I think there should be a Language flag for Bengali (also known as Bangla). As it is the national language of Bangladesh, I argue putting a flag of Bangladesh as the identification of Bengali Language. For more info about Bengali Language please see the following link:
http://en.wikipedia.org/wiki/Bengali_language
+1 for flag of Bangladesh to represent Bengali.