(Message from Assamese wikimedians via Shiju Alex)
It seems Assamese transliteration scheme added to translatewiki is meant for writing Bangla, not Assamese. "Ra" should have produced "ৰ"(assamese) but it produced "র"(bangla). Moreover I could not find keystroke for "ৱ" (pronounced 'wa') which is not there in Bangla. I also could not find out ৎ, ং and ৺(others can try). The help page redirected to a Oriya page was not of much help. So what should we do?