fc-validate: 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/fc-validate - from package: fontconfig

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

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