spd-say: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/spd-say - from package: speech-dispatcher

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