text2ngram: 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/text2ngram - from package: presage

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

Error in other languages:
text2ngram: bevel nie gevind nie
text2ngram: comandă negăsită
text2ngram: comando não encontrado
text2ngram: commande introuvable
text2ngram: command not found
text2ngram: käsku ei ole
text2ngram: không tìm thấy lệnh
text2ngram: komanda nerasta
text2ngram: Kommando nicht gefunden.
text2ngram: kommandot finns inte
text2ngram: komut yok
text2ngram: nie znaleziono polecenia
text2ngram: níor aimsíodh an t-ordú
text2ngram: no se encontró la orden
text2ngram: no s'ha trobat l'ordre
text2ngram: opdracht niet gevonden
text2ngram: parancs nem található
text2ngram: perintah tidak ditemukan
text2ngram: príkaz nenájdený
text2ngram: příkaz nenalezen
text2ngram: команда не найдена
text2ngram: командата не е открита
text2ngram: 命令找不到
text2ngram: コマンドが見つかりません