po4a-build: 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/po4a-build - from package: po4a

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

On Debian possible default full paths are:

/usr/bin/po4a-build - from package: po4a

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

Error in other languages:
po4a-build: bevel nie gevind nie
po4a-build: comandă negăsită
po4a-build: comando não encontrado
po4a-build: commande introuvable
po4a-build: command not found
po4a-build: käsku ei ole
po4a-build: không tìm thấy lệnh
po4a-build: komanda nerasta
po4a-build: Kommando nicht gefunden.
po4a-build: kommandot finns inte
po4a-build: komut yok
po4a-build: nie znaleziono polecenia
po4a-build: níor aimsíodh an t-ordú
po4a-build: no se encontró la orden
po4a-build: no s'ha trobat l'ordre
po4a-build: opdracht niet gevonden
po4a-build: parancs nem található
po4a-build: perintah tidak ditemukan
po4a-build: príkaz nenájdený
po4a-build: příkaz nenalezen
po4a-build: команда не найдена
po4a-build: командата не е открита
po4a-build: 命令找不到
po4a-build: コマンドが見つかりません