Make more core strings be translateable

Now we’re translating strings that occur in JavaScript modules.

Partially fixing #491

core/modules/language.js

@@ -0,0 +1,37 @@
+/*\
+title: $:/core/modules/language.js
+type: application/javascript
+module-type: global
+
+The $tw.Language() manages translateable strings
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Create an instance of the language manager. Options include:
+wiki: wiki from which to retrieve translation tiddlers
+*/
+function Language(options) {
+	options = options || "";
+	this.wiki = options.wiki || $tw.wiki;
+}
+
+/*
+Return a single translateable string. The title is automatically prefixed with "$:/language/"
+Options include:
+variables: optional hashmap of variables to supply to the language wikification
+*/
+Language.prototype.getString = function(title,options) {
+	options = options || {};
+	title = "$:/language/" + title;
+	return this.wiki.renderTiddler("text/plain",title,{variables: options.variables});
+};
+
+exports.Language = Language;
+
+})();