Set Moment locale to the Titanium SDK Ti.Locale.currentLocale

momentLang.js

var moment = require('alloy/moment');

// First add languages that support your application
var languages = ['ru', 'nl', 'fr', 'fr-ca'];
// Full language list:  https://github.com/appcelerator/alloy/tree/master/Alloy/builtins/moment/lang

// You must explicit way to require language files in order to compiler saw their. 
require('alloy/moment/lang/ru');
require('alloy/moment/lang/nl');
require('alloy/moment/lang/fr');
require('alloy/moment/lang/fr-ca');

function selectLanguage(lang) {
	// Not all locales with country code has corresponding file in the alloy/moment. 
	// So we will use first 2-letter language code as insurance.
	[lang.split('-')[0], lang.toLowerCase()].forEach(function(lang) {
		if(languages.indexOf(lang) !== -1) {			
			moment.lang(lang);
		}		
	});
}

exports.selectLanguage = selectLanguage;

test.js

var moment = require('alloy/moment');
var mod = require('momentLang');

Ti.API.info('current locale:', Ti.Locale.currentLocale);

Ti.API.info('current language:',  moment.lang(), 'date:', moment().format('L'));

mod.selectLanguage(Ti.Locale.currentLocale);
Ti.API.info('current language:',  moment.lang(), 'date:', moment().format('L'));

// Ask user for language or select as you need (Ti.Locale.currentLocale).
// Letter case does not matter.
mod.selectLanguage('fr-ca');
Ti.API.info('current language:',  moment.lang(), 'date:', moment().format('L'));

mod.selectLanguage('fr');
Ti.API.info('current language:',  moment.lang(), 'date:', moment().format('L'));

mod.selectLanguage('nl-BE');
Ti.API.info('current language:',  moment.lang(), 'date:', moment().format('L'));