How do I install a Korean keyboard on the Huawei Ascend G6?
Same way as on any other Android device:
- go to the Android App Store of your choice (Google Play, AppBrain, whatever) and search for "korean keyboard" (currently, 376 results)
- install the one you find suiting your needs
There are several keyboards shipping with Korean language packs, so you might as well decide picking one of those. This might possibly even come with more functionality or better usability.
Not explicitly asked for, but it will probably be your next question: You might have to "activate" that "input method" for the keyboard to show up, or even make it the default one. This can be done in Settings → Languages & Input (by "Settings" I mean the Android settings).