I have been using Scala for both server-side and Android projects. Android doesn't have such a capable VM and Scala is a little wasteful in terms of short-term objects, but using Scala while being mindful about performance implications of the code you write is still better than Java. In fact on Android you can use pretty much any language under the sun, including languages that don't run on top of the JVM. The development experience may not be as great as when using Java, sometimes you suffer from interoperability issues and so on, but for personal projects it's OK.

iOS doesn't force you to use Objective-C either. For example many top games or apps have been built in C#, by means of Unity or MonoTouch. The problem with iOS is Apple's developer agreement, as they first didn't allow apps written in anything else than Obj-C, after which they changed that to not allowing apps doing JIT compilation, but now they only enforce this rule when banning apps that download and execute code on the fly. For this reason, when embedding a WebView inside an app, Javascript will not have the same performance as Safari's Javascript engine, which is kind of stupid. So many devs prefer native compilation to avoid any problems. There's nothing wrong with iOS as a platform, what's wrong is with Apple's restrictive policies.