The first problem I see with this skin is that there are lots of untranslated strings in it, even for things (e.g. 'recentchanges') that have translations in core. These would probably be pretty easy to fix; I might try to find time, but it might be quicker for a Korean speaker. :-)
I'd say a good step would be to replace the non-i18n strings in the skin with messages (existing core ones or new skin ones, as required), and then register it with TranslateWiki.net to get more languages added.
I have commit access to the repo (as I said in task description). Can you check if this merge request will solve most of your i18n problems? (We will discuss TWN bit later, but for now we (with a librewiki hat on) have no plan to move to WMF gerrit repo and stuff because we have our own Code of Conduct and don't want to be bound by WMF Tech CoC.
As I have been for awhile, I'm busy with my real life stuff, so I don't have (not only tho) time to make a real fix if the aforementioned MR does not fix it. Happy to merge then.
I'm getting a couple of errors (with latest master of Liberty):
Undefined index: notifications-alert in skins/Liberty/LibertyTemplate.php on line 638
Undefined index: notifications-message in /home/sam/code/wikimedia/mediawiki/skins/Liberty/LibertyTemplate.php on line 639
It seems to not be checking whether Echo is installed. I'd raise a bug with the developers, but their Phabricator is all in Korean.
Other than that, I think it looks okay.