merge-changelog: 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/merge-changelog - from package: ubuntu-dev-tools

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

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