Call to undefined function __() error - phpMyAdmin with LNMP
From your log message, it seems that the mbstring
extension is missing:
/usr/share/phpmyadmin/libraries/common.inc.php(90): PMA_warnMissingExtension('mbstring', true)
Since you are using Debian, please use this to install the extension:
sudo apt-get install php7.0-mbstring