Doing interwiki links to be-x-old: is now possible; however, both wikipedias now have "Беларуская" as the name for the language. I think there should be an extra specification to distinguish the two, just like nb: does not have 'Norsk' any more, but is called 'Norsk (bokmål)'.
Does anyone who knows Belarus have good idea for the separate names? My own guess does not get further than a translation of "Belarussian (official)" for be: