which program language is good to make application like cortana or jar

Is it going to be supporting Web and mobile also? How about Windows or Linux? 

What else it will be doing more than just taking voice commands? You can use Cortana SDK to use Cortana functionality in your applications. What else you trying to do? Google, Microsoft, and other companies have open sourced their intelligent apps. 

 

Regardless, you can building anything you want in C# :) 

https://www.c-sharpcorner.com/article/why-learn-c-sharp/