The fact is that the installation files doesn’t work: when you launch it, it stalls, it doesn’t do anything.
If you right-click the package and look in its contents, you’ll find an apple script that handles all the installation process, that it’s simply an unzipping of the tarball inside the same package.
Let’s do it by hand to save some time and frustration. (Why bad (opensource) software???)
STEPS TO INSTALL BY HAND YOUR LANGUAGE PACK
1. Mount your two *.dmg , installation and language pack installation
2. Install LibreOffice (Install it in /Applications)
3. Open in a Finder window the content of Language pack installation
4. You’ll find the Contents folder. Copy it in your Desktop
It contains this:
5. Open a Terminal window (click spotlight and type Terminal and launch that app)
Type this two lines of commands:
6. cd Desktop/Contents/
and
/usr/bin/tar -C “/Applications/LibreOffice.app/” -xjf ./tarball.tar.bz2
7. Then close the Terminal and open LibreOffice, go to the preferences and choose your language (FINALLY)
This is my app translated in italian

Hope it helps! As usual, let me know how it goes for you, and also thanks for your time.