You should use the version which is appropriate for your installed
version of Qt, hence probably /usr/local/Trolltech/Qt-4.8.4/bin/lrelease
You can edit
gcconfig.pri.in to set your default:
# To compile translation you need QT tool - lrelease
# If it is not found using he defaults in src/
src.pro
# then set the full path and filename here.
#QMAKE_LRELEASE = /usr/bin/lrelease