Translation is necessary, 
but assuming that new users will be using it, I thought it would be smooth to have a function that redirects them to the client app after they open nsec[.]app from the client app and create an account. 

 Users see nsec.app in a popup, after it's all done (login/signup) the popup closes and user is back at your client app. At least that's how it should work unless there are bugs.