Same as with Relocalizer, in Heart of the Swarm you can have any voice asset and text assets, that are available only in your region (i.e. Korean - only korean text and any voice pack, etc). In the HOTS beta there is 4 available languages: english (US), french (FR), deutsch (DE) and korean (KR). These languages you can install officially without any specific steps, just go to your account page and download prefered game client.
As I said, you can have region restricted text localization (Korea? Only Korean text. Europe? Only european UI localizations then) and ANY voices (you can have korean voice pack in Europe, english voices in Korean, espanol queen in America or vice versa)
Cool that they finally do this, but me and my friends would have needed this at WoL release, when we actually played the game. :/ Sure, better late than never, but not that much better actually. The vast majority of the people that bought the game are not playing at all, or very little, at this time, and will not benefit.
Maybe I should just buy all blizzard games like 2 years after release, when it is patched into a good game...