idn: command not found

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

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

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 CentOS possible default full paths are:

/usr/bin/idn - from package: libidn

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/idn - from package: idn

You may install the required package with command apt-get install {package}

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