espeak: 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
/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 - from package: espeak

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

On Debian possible default full paths are:

/usr/bin/espeak - from package: espeak

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