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I am considered an intermediate in R and also C++ what kind of programming language I could take up and learn to make a commercial statistical software ?
Any of them, depending on environment.
If you want a web app, you want a server language (VB, C#, C++, PHP, ...) and client language - Javascript
For iOS, then it's ObjectiveC or Xamarin/C#
For Android, it's Java or Xamarin/C#
For Windows, it's almost anything except Javascript.
We don;t know what you are planning for this, so if you have good familiarity in C++, then probably that's the one to go for, unless you need to change it for a different environment.