WordPress, 英語サイト作成時に翻訳ファイルが読み込めない

/**
* Load the child themes translated strings.
*
* If the current locale exists as a .mo file in the child themes
* root directory, it will be included in the translated strings by the $domain.
*
* The .mo files must be named based on the locale exactly.
*
* @since 2.9.0
*
* @param string $domain Text domain. Unique identifier for retrieving translated strings.
* @param string $path Optional. Path to the directory containing the .mo file.
* Default false.
* @return bool True when the theme textdomain is successfully loaded, false otherwise.
*/
function load_child_theme_textdomain( $domain, $path = false ) {
    if ( ! $path )
        $path = get_stylesheet_directory();
    return load_theme_textdomain( $domain, $path );
}

/**
* Load the theme's translated strings.
*
* If the current locale exists as a .mo file in the theme's root directory, it
* will be included in the translated strings by the $domain.
*
* The .mo files must be named based on the locale exactly.
*
* @since 1.5.0
* @since 4.6.0 The function now tries to load the .mo file from the languages directory first.
*
* @param string $domain Text domain. Unique identifier for retrieving translated strings.
* @param string $path Optional. Path to the directory containing the .mo file.
* Default false.
* @return bool True when textdomain is successfully loaded, false otherwise.
*/
function load_theme_textdomain( $domain, $path = false ) {
    /**
    * Filters a theme's locale.
    *
    * @since 3.0.0
    *
    * @param string $locale The theme's current locale.
    * @param string $domain Text domain. Unique identifier for retrieving translated strings.
    */
    $locale = apply_filters( 'theme_locale', is_admin() ? get_user_locale() : get_locale(), $domain );

    $mofile = $domain . '-' . $locale . '.mo';

    // Try to load from the languages directory first.
    if ( load_textdomain( $domain, WP_LANG_DIR . '/themes/' . $mofile ) ) {
        return true;
    }

    if ( ! $path ) {
        $path = get_template_directory();
    }

    return load_textdomain( $domain, $path . '/' . $locale . '.mo' );
}

/**
* Load a .mo file into the text domain $domain.
*
* If the text domain already exists, the translations will be merged. If both
* sets have the same string, the translation from the original value will be taken.
*
* On success, the .mo file will be placed in the $l10n global by $domain
* and will be a MO object.
*
* @since 1.5.0
*
* @global array $l10n An array of all currently loaded text domains.
* @global array $l10n_unloaded An array of all text domains that have been unloaded again.
*
* @param string $domain Text domain. Unique identifier for retrieving translated strings.
* @param string $mofile Path to the .mo file.
* @return bool True on success, false on failure.
*/
function load_textdomain( $domain, $mofile ) {
    global $l10n, $l10n_unloaded;

    $l10n_unloaded = (array) $l10n_unloaded;

    /**
    * Filters whether to override the .mo file loading.
    *
    * @since 2.9.0
    *
    * @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.
    */
    $plugin_override = apply_filters( 'override_load_textdomain', false, $domain, $mofile );

    if ( true == $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 ( !is_readable( $mofile ) ) return false;

    $mo = new MO();
    if ( !$mo->import_from_file( $mofile ) ) return false;

    if ( isset( $l10n[$domain] ) )
         $mo->merge_with( $l10n[$domain] );

    unset( $l10n_unloaded[ $domain ] );

    $l10n[$domain] = &$mo;

    return true;
}