[docs] jlang() function

docs/functions/jlang.md

@@ -1,2 +1,23 @@
-## jlang()
-> Function
+## jlang($key = null, $debug = false)
+
+This function is a proxy of `Language::getInstance()`. It allows to access HTML drawing classes inside twig layouts.  
+
+1. [Parameters](#parameters)
+1. [Returns](#returns)
+2. [Examples](#examples)
+
+### Parameters <a id="parameters"></a>
+
+* `string`   **$lang**   [optional] The language to use. Default: `en-GB`
+* `boolean`  **$debug**  [optional] The debug mode. Default: `false`
+
+### Returns <a id="returns"></a>
+
+`\Joomla\CMS\Language\Language`  Language object
+
+### Examples <a id="examples"></a>
+
+```twig
+{#  Show the spanish language name #}
+{% raw %}{{ jlang('es-ES').getName() }}{% endraw %}
+```