valac-0.26: 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/valac-0.26 - from package: valac-0.26

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

Error in other languages:
valac-0.26: bevel nie gevind nie
valac-0.26: comandă negăsită
valac-0.26: comando não encontrado
valac-0.26: commande introuvable
valac-0.26: command not found
valac-0.26: käsku ei ole
valac-0.26: không tìm thấy lệnh
valac-0.26: komanda nerasta
valac-0.26: Kommando nicht gefunden.
valac-0.26: kommandot finns inte
valac-0.26: komut yok
valac-0.26: nie znaleziono polecenia
valac-0.26: níor aimsíodh an t-ordú
valac-0.26: no se encontró la orden
valac-0.26: no s'ha trobat l'ordre
valac-0.26: opdracht niet gevonden
valac-0.26: parancs nem található
valac-0.26: perintah tidak ditemukan
valac-0.26: príkaz nenájdený
valac-0.26: příkaz nenalezen
valac-0.26: команда не найдена
valac-0.26: командата не е открита
valac-0.26: 命令找不到
valac-0.26: コマンドが見つかりません