valac-0.10: 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 CentOS possible default full paths are:

/usr/bin/valac-0.10 - from package: vala

You may install the required package with command yum install {package}

Error in other languages:
valac-0.10: bevel nie gevind nie
valac-0.10: comandă negăsită
valac-0.10: comando não encontrado
valac-0.10: commande introuvable
valac-0.10: command not found
valac-0.10: käsku ei ole
valac-0.10: không tìm thấy lệnh
valac-0.10: komanda nerasta
valac-0.10: Kommando nicht gefunden.
valac-0.10: kommandot finns inte
valac-0.10: komut yok
valac-0.10: nie znaleziono polecenia
valac-0.10: níor aimsíodh an t-ordú
valac-0.10: no se encontró la orden
valac-0.10: no s'ha trobat l'ordre
valac-0.10: opdracht niet gevonden
valac-0.10: parancs nem található
valac-0.10: perintah tidak ditemukan
valac-0.10: príkaz nenájdený
valac-0.10: příkaz nenalezen
valac-0.10: команда не найдена
valac-0.10: командата не е открита
valac-0.10: 命令找不到
valac-0.10: コマンドが見つかりません