What do you need multiple languages for anyway? Java does everything you could want. Java is a powerful, object-orientated, cross-platform language, with fully developed GUIs, such as Swing.
To demonstrate the superiority of Java, I can point to such leaders in their field as Eclipse, Minecraft, and this awesome applet I saw on someone's homepage once.
Anyone still using ancient and difficult to use languages such as C++ (let alone C!) are obviously crazy, and probably should be committed for their own good before they go on spree of shooting (not just themselves, but) other people in the foot. Java makes it almost impossible to shoot yourself, let alone others, in the foot.
Moreover, because Java is licensed under the GNU GPL, you can leverage the wisdom of crowds, and the powerful "many eyes make bugs shallow" concept to be confident that Java is the best.
And with just-in-time, Java is as fast as any other language, so you don't have to worry about the speed of execution. Instead, you can focus on developer time, and Java's just faster in that regard.
With built-in, from the ground up, support for Unicode, Java is there for the future, and is ready to be used across the multiverse (as soon as those aliens get their scripts into Unicode). Beat that C, with your lack of a string type.
And if you aren't convinced, tell me why do so many top enterprises use this language? You don't see ads from Fortune 500 companies looking for Ruby "developers" do you?