my wordpress based website doesn't use the default language so i changed it in wp-config.php file, i did that because i only needed the wordpress to use my language files other than en-us, for plugins and not the theme itself. but what wordpress does is it updates the theme's language files itself, every 2 days i guess. in order to stop that and restrict wordpress from accessing wp-content/languages folder and the files in it, first i deleted all the language files and then set the folder permissions (in cpanel) to 000 or 001. it didn't work. everything changed after 2 days, automatically. folder permission changed to 755 again. then i password protected the directory and that wasn't useful either. how? when i go to wordpress dashboard/updates, there comes an option which tells me to update the translation files but when i click on it, after all the things i've done to the language folder, it updates the language files. how can wordpress do this and how can i prevent this?
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.