smplayer: 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/smplayer - from package: smplayer

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

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