Anyone that owns Flames of Vengeance or Ego Draconis, should have received a free copy of Divinity 2 : Developer's Cut. You can download this version from the larianvault.
I'm afraid savegames are incompatible between ego draconis and dragon knight saga / developer's cut though.
The fact that you can't see which languages are available of a certain product before purchase is being fixed as we speak. If you have trouble with this and want to cancel your purchase, mail support[at]larian.com