v3.1 Unescaped strings in language files after installation vs source throws 500 error

I installed the latest 3.1 version yesterday as follow:

cd /tmp
wget -O ispconfig3-dev.tar.gz "https://git.ispconfig.org/ispconfig/ispconfig3/repository/archive.tar.gz?ref=stable-3.1"
tar xzf ispconfig3-dev.tar.gz
cd ispconfig3-stable*/install

After installation navigating / calling stuff in ISPConfig under System-Interface-Main Config produces 500 errors in Apache log file like this:

[fcgid:warn] [pid 16867:tid 139865555465984] [client XXXXXX:61311] mod_fcgid: stderr: PHP Parse error:  syntax error, unexpected 's' (T_STRING) in /usr/local/ispconfig/interface/web/admin/lib/lang/en_system_config.lng on line 43, referer: https://xxxxxx:8080/index.php?phpsessid=5su4s2fbd28b06qjsffqom0ib1

cat -n /usr/local/ispconfig/interface/web/admin/lib/lang/en_system_config.lng | grep "^ *43"

gives 43 $wb["admin_mail_txt"] = 'Administrator's e-mail';

but in original source file

cat -n /tmp/ispconfig3-stable-3.1-65164295778caa2c4e623e7c8e195f2aa3560121/interface/web/admin/lib/lang/en_system_config.lng | grep "^ *39"

39 $wb['admin_mail_txt'] = 'Administrator\'s e-mail';

There seems to be something wrong in the language file installation process?