How to Add Multiple Languages Support in CodeIgniter ?

CodeIgniter comes with multi-language support, also known as internationalization which enables us to dynamically present our application’s interface in different languages without duplicating the existing source code for each language.

Configuring Multi-Language Support
First we need to configure the necessary files before we can start using language support. The CodeIgniter config file, located in the application/config directory, contains an option called language which defines the default language of the application.

<?php
$config['language'] = 'english';

CodeIgniter allows you to drop in as many languages as you want in the ../application/language/ folder. For example, if I wanted to add support for Swedish, I would create a folder inside language called "swedish". All language files must end in _lang. Let’s create some language files that contain error messages for a sample application. Create the file english/message_lang.php (it’s important that all of the language files have the suffix _lang.php). The following code contains some sample entries for the content of our language file.

Also keep in mind that for every key must be present in all of your language files. So if your ../language/english/message_lang.php file looks like this:

<?php
$lang["msg_first_name"] = "First Name";
$lang["msg_last_name"] = "Last Name";
$lang["msg_dob"] = "Date of Birth";
$lang["msg_address"] = "Address";
// more keys...

Then your ../language/swedish/message_lang.php file must look something like this:

<?php
$lang["msg_first_name"] = "Förnamn";
$lang["msg_last_name"] = "Efternamn";
$lang["msg_dob"] = "Födelsedatum";
$lang["msg_address"] = "adress";
// more keys...

Note that order does not matter in the language files. All keys are part of a larger array.

Of course, you can have multiple language files inside a single language directory. It’s recommended to group your messages into different files based on their context and purpose, and prefix your message keys with a file-specific keyword for consistency.

Loading the Language Files
There are two ways to load a language files in Codeigniter. Applying hook is the best alternative to add multi languages support.
1. Only Controller
2. Using Hook

1. Only Controller
Even though we create language files, they are not effective until we load them inside controllers. The following code shows how we can load the files inside a controller:

<?php
class TestLanguage extends CI_Controller
{
    public function __construct() {
        parent::__construct();       
        $this->lang->load("message","english");
        // or ($this->lang->load("message","swedish");)
    }
 
    function index() {
        $data["language_msg"] = $this->lang->line("msg_first_name");
        $this->load->view('language_view', $data);
    }
}

Here we’ve used a controller’s constructor to load the language file so it can be used throughout the whole class, then we reference it in the class’ index() method.

The first parameter to the lang->load() method will be the language’s filename without the _lang suffix. The second parameter, which is optional, is the language directory. It will point to default language in your config if it’s not provided here.

We can directly reference the entries of a language file using the lang->line() method and assign it’s return to the data passed into the view templates. Inside the view, we can then use the above language message as $language_msg.

<?php
$this->lang->line("language_msg");

There may be an occasion when we need to load language files directly from the views as well. For example, using language items for form labels might be considered a good reason for directly loading and accessing messages inside views. It’s possible to use the same access method for these files inside views as inside controllers.

<?php
lang("language_msg");

2. Using Hooks
Luckily, we can use CodeIgniter hooks to build a quick and effective solution for loading language files automatically for each controller. CodeIgniter calls a few built-in hooks as part of its execution process. We’ll use the post_controller_constructor hook which is called immediately after our controller is instantiated and prior to any other method calls.

We enable hooks in our application by setting the enable_hooks parameter in the main config file.

<?php
$config['enable_hooks'] = TRUE;

Then we can open the hooks.php file inside the config directory and create a custom hook as shown in the following code:

<?php
$hook['post_controller_constructor'] = array(
    'class' => 'LanguageLoader',
    'function' => 'initialize',
    'filename' => 'LanguageLoader.php',
    'filepath' => 'hooks'
);

This defines the hook and provides the necessary information to execute it. The actual implementation will be created in a custom class inside the application/hooks directory. This hooks class will load the language dynamically from the session.

<?php
class LanguageLoader
{
    function initialize() {
        $ci =& get_instance();
        $ci->load->helper('language');
 
        $site_lang = $ci->session->userdata('site_lang');

/* If you want to use cookie instead of session 
$site_lang = $ci->input->cookie('site_lang'); */

        if ($site_lang) {
            $ci->lang->load('message',$ci->session->userdata('site_lang'));
        } else {
            $ci->lang->load('message','english');
        }
    }
}

Inside the LanguageLoader class we get the active language and load the necessary language files, or we load the default language if the session key is absent. We can load multiple language files of a single language inside this class.

Switching Between Different Languages
Once we have established support for multiple languages, a link for each language can be provided to the user, generally in one of our application’s menus, which the users can click and switch the language. A session or cookie value can be used to keep track of the active language.

Let’s see how we can manage language switching using the hooks class we generated earlier. First we need to create a class to switch the language; we’ll be using a separate controller for this as shown below:

<?php
class LangSwitch extends CI_Controller
{
    public function __construct() {
        parent::__construct();
        $this->load->helper('url');
    }
 
    function switchLanguage($language = "") {
        $language = ($language != "") ? $language : "english";
        $this->session->set_userdata('site_lang', $language);
        redirect(base_url());
    }
}

Then we need to define links to switch each of the available languages.

<a href='<?php echo $base_url; ?>langswitch/switchLanguage/english'>English</a>

<a href='<?php echo $base_url; ?>langswitch/switchLanguage/swedish'>Swedish</a>

Whenever the user chooses a specific language, the switchLanguage() method of the LangSwitch class will assign the selected languages to the session and redirect the user to the home page. Now the active language will be changed in the session and will load the specific language file for the active language.

Source: http://www.sitepoint.com/multi-language-support-in-codeigniter/