wesnoth_addon_manager: 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/wesnoth_addon_manager - from package: wesnoth-tools

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

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