[TIMOB-13966] TiAPI: Select Locale for L() at runtime

// Language helper
Alloy.LanguageHelper = require('languageHelper');
Alloy.L = Alloy.LanguageHelper.fetchString;

//top of the controller
var L = require("languageHelper");

 
"#menuBtn":{
	title: L("MenuButton")
}

<Alloy>
	<Window>
		<Button id="menuBtn"></Button>
	</Window>
</Alloy>

/**
 * Language Helper
 * Makes it possible to change language at runtime 
 * @version 1.0
 */

var lookup = null;
exports.locale = Ti.App.Properties.getString('SETTING_LANGUAGE', Ti.Locale.getCurrentLanguage() );


/**
 * Private function
 * Loads the language xml file.
 * It has fallback for english if file does not exist.
 */
function loadFile() {
	lookup = {};
	
	// LOAD FILE
	var file = Ti.Filesystem.getFile(Ti.Filesystem.resourcesDirectory, 'i18n/' + exports.locale + '/strings.xml');
	if (!file.exists()) {
		file = Ti.Filesystem.getFile(Ti.Filesystem.resourcesDirectory, 'i18n/en/strings.xml');
		if (!file.exists()) {
			Ti.API.warn("Language file for both '" + exports.locale + "' and 'en' fallback do not exist");
			return;	
		}
	}
	
	// PARSE XML
	var xml_string = file.read().text;
  	var doc = Ti.XML.parseString(xml_string);
	var strings = doc.getElementsByTagName("string");
	for (var i = 0; i < strings.length; i++) {
		var node = strings.item(i);
		var value = node.text;
		if (node.hasAttributes()) {
			for (var att_index = 0; att_index < node.attributes.length; att_index++) {
				var att = node.attributes.item(att_index);
				if (att.nodeName === "name") {
					lookup[att.nodeValue] = value;
				}
			}
		}
	}
	
}

/**
 * Set the current language of the app. 
 * @param {String} language
 */
exports.setLanguage = function(language){
	if(language === null){
		return;
	}
	// clean old lookup
	exports.clear();
	
	// save language
	Ti.App.Properties.setString('SETTING_LANGUAGE', language);
	exports.locale = language;
	
	
	// parse new lookup
	loadFile();
	
	
	return lookup;
}

/**
 * Clear the parsed xml translations
 */
exports.clear = function() {
	lookup = null;
};

/**
 * Lookup function. require this at each controller
 * Example usage:
 * var L = require('languageHelper').fetchString;
 * @param {Object} string
 * @param {Object} hint
 */
exports.fetchString = function(string, hint) {
	if (lookup === null) {
		loadFile();
	}
	return lookup[string] !== undefined ? lookup[string].replace(/\\n/g, "\n") : (hint || string);
};