I think that probably the beta lottery will be available only in japanese, maybe at first, since the twitter account and the site is only in japanese.
the screen shows some UI in english (loading track - current track), but I guess they are focusing on japanese first because the programmers and audio engineers of Yamaha prefer to have a direct feedback in their native language. it also helps that a japanese user/producer has an easier access to japanese voice synth software, and again, Yamaha software engineers probably prefer to have an environment like that and a well-known community with domestic products (hardware and software) for a new beta program.
(my guess on the lottery is that probably you'll still be able to apply from overseas, but the lottery page , email messages ,the feedback and anything will be in japanese only)