I want to create an application which will be cross platform.

I know C#, WPF and native Android development, but I don't want to create an application all over again for each platform.
I wanted to ask for your recommendations for a cross platform framework for the client side.

I was suggested to use Ionic, and was told that I should also learn AngularJS as a prerequisite for Ionic. However, I don't know Javascript and I'm not a big fan of dynamic languages in general. I heard of Xamarin which lets you develop using C# which is perfect for me but it's not free.

Do you might have a recommendation for a cross platform framework for mobile development which uses a static language (maybe Java) which is also free?