I found a problem in no-wp-config screen, no-config screen dosen’t use language files at all. there are some strings of no-config-screen in POT file but they never been used/translated in the screen!
I think it’s happening because WP reads the language code from wp-config.php and WP use original strings when wp-config dosen’t exists.
in my view it’s better to look for wp-config-sample.php and read language code from it, or read the wp-content/languages for language files and use them.
what’s your idea?