spd-conf: 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-conf - from package: python3-speechd

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