na_play: 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/na_play - from package: speech-tools

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

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