If your immediate goal is to write mobile apps, my recommendation for a first language is Java. However, expect to work with console or terminal style applications on a desktop or notebook for several months to a year before you are likely to be ready for mobile app development. Maybe you could start sooner and succeed, but most people would be overwhelmed by the volume of API ("application program interface") that needs to be learned just to get a trivial app up and running. Then, each subsystem (phone, location services, network, camera, etc.) has its own set of API calls.
After getting comfortable with console/terminal programs, I suggest learning GUI ("graphical user interface") programming for the OS you use most often. It's easier to develop and debug for a desktop, and you'll be getting used to event-driven programming. Any mobile app with a user interface will be event-driven. At this point, you should also be getting comfortable working with a debugger to troubleshoot problems at runtime.
The reason for Java is that's the primary language for Android app development. Android has a narrow majority over iOS, but that argument can easily countered by the observation that Apple owners are more likely to spend money on an app. For me, the better reason to start with Android is that you can develop for it on any decent computer: PC, Mac, Linux/Unix system. Apple only supports development with Xcode on an Apple branded computer. (There are non-Apple tools, "hackintosh" computers, and such for developing on other computers, but I'd save that for when you have a better idea whether problems that arise are your coding slips or problems with your tools.)
One interesting option is that Microsoft Visual Studio offers a path to develop and publish apps for both Android and Apple iOS using their C# language. The "Community Edition" is free to use, and most indie developers can use it without license worries. This will tie you down only being able to develop on a Windows PC, though.