The bad news is that the vast majority of the "other" languages for the JVM - and this includes Clojure, JRuby, Jython, and rest - are dynamic. This means that they are either interpreted or compile to Java bytecode at run-time. Pure interpreters are fearsome slow, so these days everybody does runtime compilation.

Runtime compilation, however, won't work with Android. For licensing reasons, they use their own funky Dalvik VM, with a different instruction set to the JVM. Although you write Android code in Java, all the code in your .class files is translated into Dalvik bytecode as part of the packaging process. This is naturally incompatible with generating JVM bytecode at runtime.

The upshot, then, is that none of the big dynamic languages will run on Android, which is a big pain. Scala is an exception among the "other JVM languages". Because it is very static and doesn't have "eval" functionality, it can be completely compiled (and translated) ahead of time.

Unfortunately, even Scala has problems with Android development: For starters, the runtime libraries are over 3MB (compressed!), which is going to tax if not completely blow the memory of any phone. All that extra code between you and the VM is also going to take its toll in CPU and extra garbage collection - and on an embedded device, that's battery life you can't afford to spend.

For my money, then, the only sensible choice for Android development is native Java. This sucks, relatively speaking, but think about it as a progression: For most embedded development, C is still more or less the only sensible choice. Java is still velvet cushions and hand-holding by comparison.

However, I think the iPhone platform is the future. You have a distribution model that bypasses the carrier decks with iTunes. Which is huge because it's a pain in the ass to get on carrier decks, seeing how most NA phones are locked from installing software unless you download it directly from the carrier's portal. Then you have the fact that Apple users tend to open their wallets more for software.

You can use JavaME on it with some specific extensions, you can also use Python(at least on S60), and you can use C++(not C, if i remember correctly).

But note that the languages on this platform do not all have equal capabilities with respect to access to the underlying platform. There are some things that are just not possible...Except for the C++ part, which is the native language and thus has almost complete access to the system.

If you alreay have an iPhone, go with that, if you use a HTC/Nokia smartphone, build for that.

After you have built a few initial apps, you'll find things become much clearer and be better able to find the answers you seek.