I know that sometimes a new OS , maybe leaked or official, or even a Hybrid, may not contain all the language files, so here are all the language files you may need
1) Download the language file that you want
2) Install the OS that you want on your PC, or if it is already installed, then proceed to step 3.
3) Navigate to your OS Java folder and copy paste all the files which are in the ZIP you downloaded into that folder, and overwrite anything that comes through.
Usually, this folder is located in:
32-Bit Windows >>> C:\Program Files\Common Files\Research In Motion\Shared\Loader Files\XXX\Java (where XXX is the OS version you are installing)
64-Bit Windows >>> C:\Program Files (x86)\Common Files\Research In Motion\Shared\Loader Files\XXX\Java (where XXX is the OS version you are installing)