utf8mex: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/utf8mex - from package: texlive-lang-polish

You may install the required package with command apt-get install {package}
Error in other languages:
utf8mex: bevel nie gevind nie
utf8mex: comandă negăsită
utf8mex: comando não encontrado
utf8mex: commande introuvable
utf8mex: command not found
utf8mex: käsku ei ole
utf8mex: không tìm thấy lệnh
utf8mex: komanda nerasta
utf8mex: Kommando nicht gefunden.
utf8mex: kommandot finns inte
utf8mex: komut yok
utf8mex: nie znaleziono polecenia
utf8mex: níor aimsíodh an t-ordú
utf8mex: no se encontró la orden
utf8mex: no s'ha trobat l'ordre
utf8mex: opdracht niet gevonden
utf8mex: parancs nem található
utf8mex: perintah tidak ditemukan
utf8mex: príkaz nenájdený
utf8mex: příkaz nenalezen
utf8mex: команда не найдена
utf8mex: командата не е открита
utf8mex: 命令找不到
utf8mex: コマンドが見つかりません