load_textdomain() │ WP 1.5.0

Connects the specified translation file.

The function parses the specified .mo or .l10n.php file and adds the data from it to the WordPress translation data - to the global variable $l10n:

$l10n[ $domain ] = & $mo;

If the specified domain already exists in the data, the imported localization strings will be merged with the existing ones (combined into a single array).

The translation file must be loaded before it is used. Therefore, load_textdomain() is typically called during the plugins_loaded event.

To translate any string in WordPress, the string must have a translation, and to have it, the translation data must be loaded, among which will be the translation of the required string.

To load translation data, specifically to load the .mo or .l10n.php translation file into the global localization data, you can use:

Used By: load_muplugin_textdomain(), load_plugin_textdomain(), load_theme_textdomain()
Hooks from the function

Returns

true|false. Will return false if the .mo and .l10n.php file does not exist at the specified path. In other cases, the function will return true.

Usage

load_textdomain( $domain, $mofile, $locale );
$domain(string) (required)
A unique identifier that can be used later to reference the translation string.
$mofile(string) (required)
The absolute path to the .mo file (home/example.com/wp-content/plugins/my-plugin.mo).
$locale(string) (WP 6.1)
The locale.
Default: null (current locale)

Examples

0

#1 Line translation in WordPress

In this example, translate the string __( 'book', 'mydomain' ). It is assumed that a .mo file has already been created and has the data to translate this string:

// here the .mo file must be in the `lang` folder, which is in 
// the folder that contains the file in which this (string - code) is called.
// Connect the existing .mo file (file name: ru_RU.mo or other, depending on the locale)
add_action( 'plugins_loaded', 'load_my_textdomain' );

function load_my_textdomain(){
	$mo_file_path = dirname(__FILE__) . '/lang/'. determine_locale() . '.mo';

	load_textdomain( 'mydomain', $mo_file_path );
}

For WP versions earlier than 5.0, use get_locale() instead of determine_locale().

Now in the theme we use:

<?php _e( 'book', 'mydomain' ); ?>

The "βιβλίο" will come out for Greek locale.

0

#2 Load translation which is different from the current user locale.

There are situations where one requires a plugin translation locale to be loaded which is different from the current user locale.

For example, in multilingual websites, creating a translation of a post/widget may require some translations to be loaded for a given plugin text domain. The user locale (dashboard locale) is loaded by default, so it is important to unload that if it has been loaded already and seek the translation file to load for the text domain for the requested locale,

if ( is_textdomain_loaded( $plugin ) ) {
	unload_textdomain( $plugin );
}

$mofile = sprintf( '%s-%s.mo', $plugin, $locale );

// check the installation language path first.
$domain_path = path_join( WP_LANG_DIR, 'plugins' );
$loaded = load_textdomain( $plugin, path_join( $domain_path, $mofile ) );

// else, check the plugin language folder.
if ( ! $loaded ) { 
	$domain_path = path_join( WP_PLUGIN_DIR, "{$plugin}/languages" );
	load_textdomain( $plugin, path_join( $domain_path, $mofile ) );
}

Notes

  • Global. MO[]. $l10n An array of all currently loaded text domains.
  • Global. MO[]. $l10n_unloaded An array of all text domains that have been unloaded again.
  • Global. WP_Textdomain_Registry. $wp_textdomain_registry WordPress Textdomain Registry.

Changelog

Since 1.5.0 Introduced.
Since 6.1.0 Added the $locale parameter.

load_textdomain() code WP 6.8.1

wp-includes/l10n.php 
function load_textdomain( $domain, $mofile, $locale = null ) {
	/** @var WP_Textdomain_Registry $wp_textdomain_registry */
	global $l10n, $l10n_unloaded, $wp_textdomain_registry;

	$l10n_unloaded = (array) $l10n_unloaded;

	if ( ! is_string( $domain ) ) {
		return false;
	}

	/**
	 * Filters whether to short-circuit loading .mo file.
	 *
	 * Returning a non-null value from the filter will effectively short-circuit
	 * the loading, returning the passed value instead.
	 *
	 * @since 6.3.0
	 *
	 * @param bool|null   $loaded The result of loading a .mo file. Default null.
	 * @param string      $domain Text domain. Unique identifier for retrieving translated strings.
	 * @param string      $mofile Path to the MO file.
	 * @param string|null $locale Locale.
	 */
	$loaded = apply_filters( 'pre_load_textdomain', null, $domain, $mofile, $locale );
	if ( null !== $loaded ) {
		if ( true === $loaded ) {
			unset( $l10n_unloaded[ $domain ] );
		}

		return $loaded;
	}

	/**
	 * Filters whether to override the .mo file loading.
	 *
	 * @since 2.9.0
	 * @since 6.2.0 Added the `$locale` parameter.
	 *
	 * @param bool        $override Whether to override the .mo file loading. Default false.
	 * @param string      $domain   Text domain. Unique identifier for retrieving translated strings.
	 * @param string      $mofile   Path to the MO file.
	 * @param string|null $locale   Locale.
	 */
	$plugin_override = apply_filters( 'override_load_textdomain', false, $domain, $mofile, $locale );

	if ( true === (bool) $plugin_override ) {
		unset( $l10n_unloaded[ $domain ] );

		return true;
	}

	/**
	 * Fires before the MO translation file is loaded.
	 *
	 * @since 2.9.0
	 *
	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
	 * @param string $mofile Path to the .mo file.
	 */
	do_action( 'load_textdomain', $domain, $mofile );

	/**
	 * Filters MO file path for loading translations for a specific text domain.
	 *
	 * @since 2.9.0
	 *
	 * @param string $mofile Path to the MO file.
	 * @param string $domain Text domain. Unique identifier for retrieving translated strings.
	 */
	$mofile = apply_filters( 'load_textdomain_mofile', $mofile, $domain );

	if ( ! $locale ) {
		$locale = determine_locale();
	}

	$i18n_controller = WP_Translation_Controller::get_instance();

	// Ensures the correct locale is set as the current one, in case it was filtered.
	$i18n_controller->set_locale( $locale );

	/**
	 * Filters the preferred file format for translation files.
	 *
	 * Can be used to disable the use of PHP files for translations.
	 *
	 * @since 6.5.0
	 *
	 * @param string $preferred_format Preferred file format. Possible values: 'php', 'mo'. Default: 'php'.
	 * @param string $domain           The text domain.
	 */
	$preferred_format = apply_filters( 'translation_file_format', 'php', $domain );
	if ( ! in_array( $preferred_format, array( 'php', 'mo' ), true ) ) {
		$preferred_format = 'php';
	}

	$translation_files = array();

	if ( 'mo' !== $preferred_format ) {
		$translation_files[] = substr_replace( $mofile, ".l10n.$preferred_format", - strlen( '.mo' ) );
	}

	$translation_files[] = $mofile;

	foreach ( $translation_files as $file ) {
		/**
		 * Filters the file path for loading translations for the given text domain.
		 *
		 * Similar to the {@see 'load_textdomain_mofile'} filter with the difference that
		 * the file path could be for an MO or PHP file.
		 *
		 * @since 6.5.0
		 * @since 6.6.0 Added the `$locale` parameter.
		 *
		 * @param string $file   Path to the translation file to load.
		 * @param string $domain The text domain.
		 * @param string $locale The locale.
		 */
		$file = (string) apply_filters( 'load_translation_file', $file, $domain, $locale );

		$success = $i18n_controller->load_file( $file, $domain, $locale );

		if ( $success ) {
			if ( isset( $l10n[ $domain ] ) && $l10n[ $domain ] instanceof MO ) {
				$i18n_controller->load_file( $l10n[ $domain ]->get_filename(), $domain, $locale );
			}

			// Unset NOOP_Translations reference in get_translations_for_domain().
			unset( $l10n[ $domain ] );

			$l10n[ $domain ] = new WP_Translations( $i18n_controller, $domain );

			$wp_textdomain_registry->set( $domain, $locale, dirname( $file ) );

			return true;
		}
	}

	return false;
}

textdomain (mo po files)

localize (l10n i18n Internationalization localization)

Localization