diff -r 000000000000 -r 6474c204b198 addon-sdk/source/lib/sdk/l10n/properties/core.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/addon-sdk/source/lib/sdk/l10n/properties/core.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,79 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const { Cu } = require("chrome");
+const { newURI } = require('../../url/utils')
+const { getRulesForLocale } = require("../plural-rules");
+const { getPreferedLocales } = require('../locale');
+const { rootURI } = require("@loader/options");
+const { Services } = Cu.import("resource://gre/modules/Services.jsm", {});
+
+const baseURI = rootURI + "locale/";
+const preferedLocales = getPreferedLocales(true);
+
+function getLocaleURL(locale) {
+  // if the locale is a valid chrome URI, return it
+  try {
+    let uri = newURI(locale);
+    if (uri.scheme == 'chrome')
+      return uri.spec;
+  }
+  catch(_) {}
+  // otherwise try to construct the url
+  return baseURI + locale + ".properties";
+}
+
+function getKey(locale, key) {
+  let bundle = Services.strings.createBundle(getLocaleURL(locale));
+  try {
+    return bundle.GetStringFromName(key) + "";
+  }
+  catch (_) {}
+  return undefined;
+}
+
+function get(key, n, locales) {
+  // try this locale
+  let locale = locales.shift();
+  let localized;
+
+  if (typeof n == 'number') {
+    if (n == 0) {
+      localized = getKey(locale, key + '[zero]');
+    }
+    else if (n == 1) {
+      localized = getKey(locale, key + '[one]');
+    }
+    else if (n == 2) {
+      localized = getKey(locale, key + '[two]');
+    }
+
+    if (!localized) {
+      // Retrieve the plural mapping function
+      let pluralForm = (getRulesForLocale(locale.split("-")[0].toLowerCase()) ||
+                        getRulesForLocale("en"))(n);
+      localized = getKey(locale, key + '[' + pluralForm + ']');
+    }
+
+    if (!localized) {
+      localized = getKey(locale, key + '[other]');
+    }
+  }
+
+  if (!localized) {
+    localized = getKey(locale, key);
+  }
+
+  if (localized) {
+    return localized;
+  }
+
+  // try next locale
+  if (locales.length)
+    return get(key, n, locales);
+
+  return undefined;
+}
+exports.get = function(k, n) get(k, n, Array.slice(preferedLocales));