footnotes/class/language.php

<?php
/**
 * Loads text domain of current or default language for localization.
 *
 * @filesource
 * @author Stefan Herndler
 * @since 1.5.0 14.09.14 17:47
 *
 *
 * @lastmodified 2021-02-08T1914+0100
 *
 * @since 2.0.0  Bugfix: Localization: correct function call apply_filters() with all required arguments after PHP 7.1 promoted warning to error, thanks to @matkus2 bug report and code contribution.
 * @since 2.1.6  Bugfix: Localization: conform to WordPress plugin language file name scheme, thanks to @nikelaos bug report.
 */

/**
 * Loads text domain of current or default language for localization.
 *
 * @author Stefan Herndler
 * @since 1.5.0
 */
class MCI_Footnotes_Language {

    /**
     * Register WordPress Hook.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     */
    public static function registerHooks() {
        add_action('plugins_loaded', array("MCI_Footnotes_Language", "loadTextDomain"));
    }

    /**
     * Loads the text domain for current WordPress language if exists.
     * Otherwise fallback "en_GB" will be loaded.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     *
     *
     * - Bugfix: Correct function call apply_filters() with all required arguments after PHP 7.1 promoted warning to error, thanks to @matkus2 bug report and code contribution.
     *
     * @since 2.0.0
     * @datetime 2020-10-26T1609+0100
     *
     * @contributor @matkus2
     * @link https://wordpress.org/support/topic/error-missing-parameter-if-using-php-7-1-or-later/
     *
     * Add 3rd (empty) argument in apply_filters() to prevent PHP from throwing an error:
     * “Fatal error: Uncaught ArgumentCountError: Too few arguments to function apply_filters()”
     *
     * Yet get_locale() is defined w/o parameters in wp-includes/l10n.php:30, and
     * apply_filters() is defined as apply_filters( $tag, $value ) in wp-includes/plugin.php:181.
     * @link https://developer.wordpress.org/reference/functions/apply_filters/
     *
     * But apply_filters() is defined with a 3rd parameter (and w/o the first one) in
     * wp-includes/class-wp-hook.php:264, as public function apply_filters( $value, $args ).
     *
     * Taking it all together, probably the full function definition would be:
     * public function apply_filters( $tag, $value, $args ).
     * In the case of get_locale(), $args is empty.
     *
     * The bug was lurking in WP. PHP 7.1 promoted the warning to an error.
     * @link https://www.php.net/manual/en/migration71.incompatible.php
     * @link https://www.php.net/manual/en/migration71.incompatible.php#migration71.incompatible.too-few-arguments-exception
     */
    public static function loadTextDomain() {

        // if language file with localization exists:
        if ( self::load( apply_filters( 'plugin_locale', get_locale(), '' ) ) ) {
            return;
        }
        // else fall back to British English:
        self::load( "en_GB" );
    }

    /**
     * Loads a specific text domain.
     *
     * @author Stefan Herndler
     * @since 1.5.1
     * @param string $p_str_LanguageCode Language Code to load a specific text domain.
     * @return bool
     *
     *
     * - Bugfix: Localization: conform to WordPress plugin language file name scheme, thanks to @nikelaos bug report.
     *
     * @since 2.1.6
     * @datetime 2020-12-08T1931+0100
     *
     * @reporter @nikelaos
     * @link https://wordpress.org/support/topic/more-feature-ideas/
     *
     * That is done by using load_plugin_textdomain():
     * “The .mo file should be named based on the text domain with a dash, and then the locale exactly.”
     * @see wp-includes/l10n.php:857
     */
    private static function load($p_str_LanguageCode) {
        return load_plugin_textdomain(
            MCI_Footnotes_Config::C_STR_PLUGIN_NAME,
            // This argument only fills the gap left by a deprecated argument (since WP2.7):
            false,
            // The plugin basedir is provided; trailing slash would be clipped:
            MCI_Footnotes_Config::C_STR_PLUGIN_NAME . '/languages'
        );
    }
}