Updating CONTRIBUTING.md

CONTRIBUTING.md

@@ -9,8 +9,10 @@ Contributions are welcome, and are accepted via pull requests. Please review the
   * Remember that we follow SemVer. If you are changing the behaviour, or the public api, you may need to update the docs.
   * Send a coherent commit history, making sure each individual commit in your pull request is meaningful. If you had to make multiple intermediate commits while developing, please squash them before submitting.
   * You may also need to rebase to avoid merge conflicts.
-  * Translations : After you made your translations, ensure that you added your locale key (alphabetical order) at [line](https://github.com/ARCANEDEV/LogViewer/blob/master/tests/TestCase.php#L29) in the `tests/TestCase.php` file for tests.
-
+  * **Translations :**
+    * After you made your translations, ensure that you added your locale key in alphabetical order at [line](https://github.com/ARCANEDEV/LogViewer/blob/master/tests/TestCase.php#L29) in the `tests/TestCase.php` file for the tests.
+    * The locale key must be a [ISO 639-1 code](https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes), check also [caouecs/Laravel-lang package](https://github.com/caouecs/Laravel-lang/).
+
 ## Running Tests
 
 You will need an install of [Composer](https://getcomposer.org) before continuing.