msgmerge: 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 CentOS possible default full paths are:

/usr/bin/msgmerge - from package: gettext

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

On Debian possible default full paths are:

/usr/bin/msgmerge - from package: gettext

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

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