That's going to depend on a lot of factors, really. Different programmers find different languages appealing.
As for which language to choose, the obvious choice would be Java itself. However, you could in principle use any language which runs on the Java JVM platform, which includes Jython (a Python port to the JVM), JRuby (the same, for Ruby), Scala, Groovy, Kawa Scheme, and Clojure. Which of those would be best for you? That's really not something I can say easily; my own preferences would be for either Kawa or Clojure, for example, but a lot of people find the unusual syntax of the Lisp languages to be off-putting. IME, most people do well with either Python or Ruby as their first language, so one of those might be the place to start.
The real question is, will the language you want run under J2ME? As far as I am aware, Java and Scala are the only ones which do to date.
Mind you, as far as I am aware, J2ME is something of a dead issue for mobile development at this point; most smartphone development is being done on other platforms, such as Android (which uses Google's own Java virtual machine and development libraries) or iOS (which, last I'd heard, can only be programmed with Objective-C, and has to be developed from a Mac). While there are still plenty of J2ME devices around, they aren't neccessarily ones you'd have games on.