language codes have been changed from CS to CZ. but there is no update for lang_settings.php.
Here the files are named i.e. languages/lang.cs.php instead of *.cz.php.
This causes that CZ language always displays English.
You should be using the "SVN" version of PGV. Download and upgrade instructions are in a recent Help topic whose title begins with "Repost: ...". However, this will NOT fix your problem.
There is no automatic upgrade for the lang_settings.php file when you upgrade from one version of PGV to another. Usually, that does not cause a problem. However, as you've discovered, there is a problem when the language codes change. Fortunately, this is an extremely rare occurrence. It's simply not worth trying to create a program for that.
To correct the problem, you need to delete file "index/lang_settings.php". You can delete file "index/lang_settings.old" too -- this one is useless.
After having deleted the faulty "lang_settings.php" file, launch PhpGedView (it will start in English), log in as Admin, and then use the "Configure Supported Languages" admin menu option. Set the languages your site will support and adjust the language configurations to suit your requirements.