For some reason I have a mental block and can’t seem to remember this, but instead of using dism to install language packs on Windows 7 or above, like this…
dism /online /add-package /packagepath:<path to language pack .cab file>
…you can also simply rename the .cab language pack file to have the .mlc file extension and double-click it.
There’s yet another way too, and that’s to run the lpksetup.exe utility and point it at your .cab file I think. Haven’t tried that though as I think the .mlc method is easier.