added doc about translating message.

docs/internals/translations.md

@@ -7,12 +7,15 @@ where contribution is very welcome are documentation and framework messages.
 Framework messages
 ------------------
 
-Framework has two types of messsages: exceptions that are intended to developer and are never translated and messages
+Framework has two types of messages: exceptions that are intended to developer and are never translated and messages
 that are actually visible to end user such as validation errors.
 
 In order to start with message translation:
 
-1. Check `framework/messages/config.php` and make sure your language is listed in `languages`.
+1. Check `framework/messages/config.php` and make sure your language is listed in `languages`. If not,
+   add your language there (remember to keep the list in alphabetical order). The format of language code
+   should follow [IETF language tag spec](http://en.wikipedia.org/wiki/IETF_language_tag), for example,
+   `ru`, `zh-CN`.
 2. Go to `framework` and run `yii message/extract messages/config.php`.
 3. Translate messages in `framework/messages/your_language/yii.php`. Make sure file is saved using UTF-8 encoding.
 4. [Make a pull request](https://github.com/yiisoft/yii2/blob/master/docs/internals/git-workflow.md).

framework/messages/config.php

@@ -7,7 +7,7 @@ return [
 	'messagePath' => __DIR__,
 	// array, required, list of language codes that the extracted messages
 	// should be translated to. For example, ['zh-CN', 'de'].
-	'languages' => ['ar', 'da', 'de', 'es', 'it', 'ja', 'pl', 'pt-BR', 'ro', 'ru', 'sr','sr-Latn', 'zh-CN'],
+	'languages' => ['ar', 'da', 'de', 'es', 'it', 'ja', 'pl', 'pt-BR', 'ro', 'ru', 'sr', 'sr-Latn', 'zh-CN'],
 	// string, the name of the function for translating messages.
 	// Defaults to 'Yii::t'. This is used as a mark to find the messages to be
 	// translated. You may use a string for single function name or an array for