f-irc: 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/f-irc - from package: f-irc

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

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