Hacky solution: Yeoman generator nested prompt...

index.js

'use strict';
var yeoman = require('yeoman-generator');
var chalk = require('chalk');
var yosay = require('yosay');

module.exports = yeoman.Base.extend({
  prompting: function () {
    // Have Yeoman greet the user.
    this.log(yosay(
      'Welcome to the amazing ' + chalk.red('generator-try-mb') + ' generator!'
    ));

    var prompts = [{
      type: 'checkbox',
      name: 'someAnswer',
      message: 'select languages',
	  choices: ["en","it","de","fr","es","pt","ru"],
      default: []
    }];

	var questionary = this;

    return this.prompt(prompts).then(function (props) {
		// To access props later use this.props.someAnswer;
		/*
	  if(props.someAnswer.length>0){
		  	var questions2=[];
			  var i=0;
			for(i=0; i<props.someAnswer.length; i++){

				questions2[i] = {
					type:'input',
					name:'two'+props.someAnswer[i],
					message:'translation of "this thing" in  '+props.someAnswer[i],
					default: ""
				};
			}
			
			this.prompt(questions2).then(function(props2){
				this.props2=props2;
			}.bind(this));
		}
		*/
		this.props = props;

    }.bind(this));
  },
  configuring: function (){

  },
  promptingSecond:function(){
	  // this should fall in the default group
	var props = this.props;
	if(props.someAnswer.length>0){
		var questions2=[];
			var i=0;
		for(i=0; i<props.someAnswer.length; i++){

			questions2[i] = {
				type:'input',
				name:'two'+props.someAnswer[i],
				message:'translation of "this thing" in  '+props.someAnswer[i],
				default: ""
			};
		}
		
		return this.prompt(questions2).then(function(props2){
			this.props2 = props2;
		}.bind(this));
	}
  },
  conflicts: function (){

  },
  writing: function () {
	  this.log(JSON.stringify(this.props));
	  this.log(JSON.stringify(this.props2));
    this.fs.copy(
      this.templatePath('dummyfile.txt'),
      this.destinationPath('dummyfile.txt')
    );
  },

  install: function () {
    // this.installDependencies();
  },

  end: function(){
	  this.log(" bye! ");
	  return this;
  }
});

I've created a "promptingSecond" (line 51) task, that will fall after prompting, cause it will fall in the default group but i don't really like it cause it can be strange if there are nested loops questions like...

how many elements?
how many thing in the first element?
name of the 1.1: ___
name of the 1.2: ___ 
...

how many thing in the second element?
name of the 2.1: ___
name of the 2.2: ___ 
...

...