uninstall.php

<?php
/**
 * Fired when the plugin is uninstalled.
 *
 * @author     WP-Translations Team
 * @link       https:wp-translations.pro
 * @since      1.0.0
 *
 * @package    WPT_Custom_Mo_File
 */

// Exit if accessed directly.
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}


// Delete WPT_CUSTOMOFILE options.
if ( is_multisite() ) {

	global $wpdb;
	foreach ( $wpdb->get_col( "SELECT blog_id FROM $wpdb->blogs" ) as $blog_id ) { // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching,WordPress.WP.GlobalVariablesOverride.Prohibited
		switch_to_blog( $blog_id );
		delete_option( 'wpt_customofile_options' );
		restore_current_blog();
	}
} else {
	delete_option( 'wpt_customofile_options' );
}

/**
 * Remove all mo files.
 *
 * @since 1.0.0
 *
 * @param string $dir   Filename.
 *
 * @return void
 */
function wpt_customofile_rrmdir( $dir ) {

	if ( ! is_dir( $dir ) ) {
		unlink( $dir );
		return;
	}

	$globs = glob( $dir . '/*', GLOB_NOSORT );

	if ( $globs ) {
		foreach ( $globs as $file ) {
			is_dir( $file ) ? wpt_customofile_rrmdir( $file ) : unlink( $file );
		}

		// Unset unused variable.
		unset( $globs );
	}
	rmdir( $dir );
}


$wpt_customofile_upload_dir = wp_upload_dir();

$wpt_customofile_upload_dir = $wpt_customofile_upload_dir['basedir'] . '/wpt-custom-mo-file';

wpt_customofile_rrmdir( $wpt_customofile_upload_dir );