Russian course For iOS ?
How many users does the Russian course for English speakers need for iOS/Mobile
It depends on how stable it is. Once they stop getting x amount of error reports, they'll port it to the app.
The course graduating from beta to stable version depends not on how many users are taking the Russian course, but on how many alternative answers have been added so that the amount of reports drops below x amount and the course is considered to read for release by duolingo.