apertium-gen-lextormono: 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/apertium-gen-lextormono - from package: apertium

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