ch_lab: 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/ch_lab - from package: speech-tools

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

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