A TinyMCE plugin which adds a custom dropdown menu.

plugin.js

(function() {
	var languages = ['css', 'php', 'html', 'javascript'];
	
	tinymce.PluginManager.add( 'prism', function( editor ){
		
		var items = [];

		tinymce.each( languages, function( languageName ){
			items.push({
				text: languageName,
				onclick: function(){
					var content = tinyMCE.activeEditor.selection.getContent();
					editor.insertContent( '<pre><code class="language-' + languageName + '">' + content + '</code></pre>' );
				}
			});
		});

		editor.addButton( 'prism', {
			type: 'menubutton',
			text: 'Prism',
			icon: 'code',
			menu: items
		});

	});
})();