The Nusach of this app is Nusach Ari of the Adha”z.
Adding other Nuschaos is something we are seriously looking into, but it is not likely to happen in the near future.
An Android version of the Siddur is being worked on, there is no release date yet.
The Nusach itself is only in Hebrew in this Siddur app. At the moment there are no plans for an English version (or any other language).
If the above information did not clarify your issue, please email [email protected]. Thanks!