kde-nm-connection-editor: 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 Debian possible default full paths are:

/usr/bin/kde-nm-connection-editor - from package: plasma-nm

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

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