It sounds illogical to ask for a Bengali sub board for Bengali translation and press release because we don't have any local boards yet. But the way the Bengali board is hammered with translated topics and news source posts, it looks like spamming to many of us.
This is a good request you have just raised to ask the permission for granting you a sub board, but to make your request more presentable, let me ask you to do one additional task, you can edit the whole post and make it looks more official because you're directing it to the admin, show some additional informations or statistics of active members you have engage in your discussion and many more other things to add up to your chances of receiving higher considerations.