It was not an easy task to search for all steps needed to create a WordPress plugin that supports multiple language.

So I’m listing here all the steps I learned in the proccess of developing an i18n WordPress plugin.

Step 1 : Choose a Domain For Your Plugin Texts

A domain is a name space you choose to facilitate your texts under. And you control when these texts will be available.

What I did was to add a function when the plugin was loaded

add_action('plugins_loaded', 'my_custom_init_function');

This function is called when the plugins are loaded, In ‘my_custom_init_function’ I load the text with the domain name I picked for the texts:

function my_custom_init_function() {
 $plugin_dir = basename(dirname(__FILE__));
 load_plugin_textdomain( 'my-custom-domain-name', false, $plugin_dir . '/language');

the load_plugins_textdomain load the translation from the third parameter location. I chose to put the translation files inside the plugin so it will be part of the plugin package. I’ll cover on how to create the translation files in Step 3

Step 2 : Wrap All Your Texts With The Translation Function

We need to declare which text is for translation. We do that with the __ (double underscore) function. The second parameter of the __ function is the text domain we chose in step 1. So an example usage will be:

__( 'Some sample text', 'my-custom-domain-name' )

And we are done! The only thing that is left is to do the actual translation – That will be done in the next step

Step 3 : Translate Your WordPress Plugin

Translation in WordPress is made with .po and .mo files. You use the .po files in a text editor and these files are converted to .mo files which are binary files. You can save a lot of headache by letting some other plugin to create those files for you. I played with a few plugins and the one that I liked the most was Codestyling Localization. With this plugin you translate your plugin directly from the admin panel ( tools > localization ) and you can also generate the .mo file in one click.

More Information

You can have multiple text domains in your plugin, that make sense if you have different areas your plugin is running under and than you can make a text domain for each area. For example if your plugin is running in the admin panel and in a blog post it make sense to separate the two into two text domains.