fst-generate: 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 Debian possible default full paths are:

/usr/bin/fst-generate - from package: sfst

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