Cross platform apps are primarily developed in HTML, CSS and Javascript (the programming languages used to build websites) and then compiled into the native code required by Apple and Android apps. We say 'primarily' because some functionality still needs to be built in the core native language in order for it to work properly. Native apps are built directly in Swift or Objective C for Apple, and Java for Android apps.
Generally speaking native built apps will perform better than cross platform provide a more standard look and feel for the particular platform, and provide credibility for practicality that demands deeper interaction with device hardware.
However, it is important to assess each app on a case by case basis, as building once for both platforms is more cost effective. Newer programming languages such as ReactNative are providing additional opportunities to reduce the cost of development and maintenance.
The cost of voice-enabled application development depends from project to project, on the basis of the application platform and the kind of features and functionalities you need in the app. Reach us with your project requirements to get a cost estimation for your project.