espeak-synthesis-driver: 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/espeak-synthesis-driver - from package: gnome-speech-espeak

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

On Debian possible default full paths are:

/usr/bin/espeak-synthesis-driver - from package: libgnome-speech7

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

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