I think it is debatable if you need a French, German or Norwegian version to improve sales.
Being European myself I know that people from these countries have very good English language skills.
With a product as yours where you target very special interest groups you can assume that people speak English!
Yes, if you put Nistune into French you have no idea, but that's only because you translated common terns into French.
I would agree on the Japanese translation, having worked in Tokyo I know that English is not commonly spoken.
But (as said) Dutch, Germans, Norwegians, Finnish, or people from Denmark have very good language skills.
Anyhow, just might thoughts on this; I just hope bug fixes, the overhaul of the GUI, and new releases will not be delayed