jalv.gtk3: command not found

Have You tried accessing the binary with the full path?

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/jalv.gtk3 - from package: jalv

You may install the required package with command apt-get install {package}
Error in other languages:
jalv.gtk3: bevel nie gevind nie
jalv.gtk3: comandă negăsită
jalv.gtk3: comando não encontrado
jalv.gtk3: commande introuvable
jalv.gtk3: command not found
jalv.gtk3: käsku ei ole
jalv.gtk3: không tìm thấy lệnh
jalv.gtk3: komanda nerasta
jalv.gtk3: Kommando nicht gefunden.
jalv.gtk3: kommandot finns inte
jalv.gtk3: komut yok
jalv.gtk3: nie znaleziono polecenia
jalv.gtk3: níor aimsíodh an t-ordú
jalv.gtk3: no se encontró la orden
jalv.gtk3: no s'ha trobat l'ordre
jalv.gtk3: opdracht niet gevonden
jalv.gtk3: parancs nem található
jalv.gtk3: perintah tidak ditemukan
jalv.gtk3: príkaz nenájdený
jalv.gtk3: příkaz nenalezen
jalv.gtk3: команда не найдена
jalv.gtk3: командата не е открита
jalv.gtk3: 命令找不到
jalv.gtk3: コマンドが見つかりません