sp15tax_newTermSet.js

$(document).ready(function(){   
  
	var scriptbase = _spPageContextInfo.webServerRelativeUrl + "_layouts/15/";
	
	$.getScript(scriptbase + "SP.Runtime.js",
        function () {
            $.getScript(scriptbase + "SP.js", function(){
            
            	$.getScript(scriptbase + "SP.Taxonomy.js", execOperation);

            });
        }
    );

});

function execOperation(){
	
	//Current Context
    var context = SP.ClientContext.get_current();
	
    //Current Taxonomy Session
    var taxSession = SP.Taxonomy.TaxonomySession.getTaxonomySession(context);
    
    //Term Stores
    var termStores = taxSession.get_termStores();
    
    //Term Store under which to create the Term Set.
    var termStore = termStores.getByName("Taxonomy_Dmxzz8tIBzk8wNVKQpJ+xA==");    	
	
	  //Get group by GUID
	  var peopleGroup = termStore.getGroup("97eaa7b8-9778-4f61-acb3-7f47abba13c3");
	
		//Create New Term Set in Group with Name, New GUID and LCID
		var newTermSet = peopleGroup.createTermSet("New TermSet Name","49dac247-d315-4065-8718-e8c3f50e7dcd",1033);
	
		context.load(newTermSet);
		
		context.executeQueryAsync(function(){
	
  		console.log(newTermSet.get_name());
   		
		},function(sender,args){
	
			console.log(args.get_message());
	
		});

}