adding normalizeLanguage api

lib/i18n.js

@@ -366,6 +366,15 @@ exports.languageFrom = languageFrom = function(locale) {
   }
 };
 
+/**
+ * Given a language code, return a normalized language code.
+ * @param  {String} language A language code. For example, 'en-us'.
+ * @return {String}          A normalized language code, such as 'en-US'.
+ */
+exports.normalizeLanguage = normalizeLanguage = function (language) {
+  return languageFrom(localeFrom(language));
+};
+
 /**
  * Given a locale code, return a normalized locale code.
  * @param  {String} locale A locale code. For example, 'en_us'.

tests/i18n-tests.js

@@ -43,6 +43,65 @@ suite.addBatch({
   }
 });
 
+suite.addBatch({
+  "a lowercase language code": {
+    topic: function () {
+      return i18n.normalizeLanguage("en");
+    },
+    "is normalized to itself": function (err, str) {
+      assert.equal(str, "en");
+    }
+  },
+  "an uppercase language code": {
+    topic: function () {
+      return i18n.normalizeLanguage("EN");
+    },
+    "is normalized to lowercase": function (err, str) {
+      assert.equal(str, "en");
+    }
+  },
+  "a two part langauge code": {
+    topic: function () {
+      return i18n.normalizeLanguage("en-us");
+    },
+    "is normalized to 'xx-XX' format": function (err, str) {
+      assert.equal(str, "en-US");
+    }
+  },
+  "a three char language code": {
+    topic: function () {
+      return i18n.normalizeLanguage("HaW");
+    },
+    "returns the same three char code in lowercase": function (err, str) {
+      assert.equal(str, "haw");
+    }
+  },
+  "a three char language code with two parts": {
+    topic: function () {
+      return i18n.normalizeLanguage("SoN-Ml");
+    },
+    "is normalized to 'xxx-XX' format": function (err, str) {
+      assert.equal(str, "son-ML");
+    }
+  },
+  "A language with three parts": {
+    topic: function () {
+      return i18n.normalizeLanguage("ja-JP-mac");
+    },
+    "ignores the second part and returns a locale in 'xx-Xxx' format": function (err, str) {
+      assert.equal(str, "ja-Mac");
+    }
+  },
+  "A language with an underscore": {
+    topic: function () {
+      return i18n.normalizeLanguage("sR_LatN");
+    },
+    "is normalized to a hyphen in correct 'xx-XXXX' format": function (err, str) {
+      assert.equal(str, "sr-Latn");
+    }
+  }
+});
+
 suite.addBatch({
   "a lowercase locale code": {
     topic: function () {