gtk-launch: 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/gtk-launch - from package: libgtk-3-bin

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

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