swiften-config: 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 CentOS possible default full paths are:

/usr/bin/swiften-config - from package: swiften-devel

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/swiften-config - from package: libswiften-dev
/usr/lib/debug/usr/bin/swiften-config - from package: swift-im-dbg

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