platex: 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/platex - from package: texlive-east-asian

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

On Debian possible default full paths are:

/usr/bin/platex - from package: texlive-lang-japanese

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

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