unaccent: 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

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/unaccent - from package: unaccent

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