gnome-subtitles: 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/gnome-subtitles - from package: gnome-subtitles

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

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