Assamese is NOT a dialect of Bengali. It is older than Bengali and infact the first non-Sanskrit language to which Ramayana was translated to. The Assamese script itself is in a continuous development since 5th century.
The earliest extent translation of the Ramayana is the Tamil Kampan Ramayana from the late 12th century. The might have been a Khmer translation earlier. The Assamese Kotha Ramayana is about two hundred years later. The Jain Ardhamagghadi Ramayana is very old, perhaps older than the Valmikiramayana!
I stand corrected about Assamese's relationship with Bengali.
I stand corrected about Assamese's relationship with Bengali.