i know it’s a bit late but i’m going to answer it. if folder permissions get changed by themselves even after you password-protect them then i assume there is some serious problems with your Cpanel and your hosting. I’ve had a problem like this in my project but not on WordPress and it turned out to be a problem at their end.
in the latest version of WordPress, there is an option to set your default language for your WordPress dashboard, website and plugins and it will override the options on wp-config.php so you don’t need to modify that file everytime you update your wordpress site. the only thing you need is to put required files in each plugins/themes language folder with the correct country flag. hope that helps.