Yes : you can delete the language files you don't need in "Apps\LibreOffice\App\LibreOffice\Basis\program\resource".
That's what I did to reach 378 MB total.
The tricky part, though, is how to select the files to delete, among the ones you want to keep, as all the files are named "x...xCC.res", where "CC" is the Country Code (en, fr, ja, etc...)
For that matter, I used an exclusion filter in Xplorer2, to select (for deletion) ALL files BUT the ones to keep.
If your selection and deletion process was OK, then you should get 77 files for each language you kept.
(For instance, I kept English-US, French, and Japanese, so I now have 3 x 77 = 231 files remaining).
Hope I explained it clearly enough...