Thanks for the experimental language selection, it's great.
Here are some folders/files that LOP missed or where users could manually make some careful adjustments to slim the install down (my base language is "Deutsch"):
App\DefaultData\settings\user\config\
App\libreoffice\Basis\presets\config\
App\libreoffice\Basis\program\resource\
App\libreoffice\Basis\share\autocorr
App\libreoffice\Basis\share\basic\Depot
App\libreoffice\Basis\share\registry
App\libreoffice\Basis\share\registry\res
App\libreoffice\Basis\share\template\wizard\letter\
App\libreoffice\program\resource
App\libreoffice\program\shell\backing_left-pt_BR.png
App\libreoffice\readmes
App\libreoffice\share\extensions\NLPSolver\locale
App\libreoffice\share\extensions\presenter-screen\help
App\libreoffice\share\extensions\wiki-publisher\help
App\libreoffice\share\registry
App\Manual
Data\settings\user\config
The issue is that some of those folders are problematic and will actually cause operational issues within LibreOffice if you remove the bits in them. Others are too small to worry about (readmes for example).
I would be interested to see what happens when you remove all of that and attempt to select another language, though.
Sometimes, the impossible can become possible, if you're awesome!
LibreOffice Portable 3.5.3 includes a greatly improved language remover that cuts install size down to 250MB. Some of the above suggestions were used.
Sometimes, the impossible can become possible, if you're awesome!