According to the Google Blog news google adsense now supported Bengali (Bangla), but it is heard most of bengali application for google adsense is not approved due to unsupported language again. I am also experienced, I requested to get adsense for my Bengali website, but I have been declined due to unsupported language issue. Funny thing, do not understand, what is the logic.
Google Blog Announcement Url - https://adsense.googleblog.com/2017/09/adsense-now-understands-bengali-bangla.html
My bangla blog Url - http://www.prozokti.com
I have rejected for this issue, Show screenshot bellow -