lrelease: 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/lib64/qt-3.3/bin/lrelease - from package: qt3-devel
/usr/lib/qt-3.3/bin/lrelease - from package: qt3-devel
/usr/lib64/qt5/bin/lrelease - from package: qt5-linguist
/usr/lib64/qt4/bin/lrelease - from package: qt-devel
/usr/lib/qt4/bin/lrelease - from package: qt-devel

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

On Debian possible default full paths are:

/usr/lib/x86_64-linux-gnu/qt4/bin/lrelease - from package: qt4-linguist-tools
/usr/share/qt4/bin/lrelease - from package: qt4-linguist-tools
/usr/bin/lrelease - from package: qtchooser
/usr/lib/x86_64-linux-gnu/qt5/bin/lrelease - from package: qttools5-dev-tools

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

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