Are you talking about the text that appears randomly near the chatbox and is different colored? If so, that'd be a SourceMod plugin. Something like
this ShowSyncHudText example plugin is a good starting point. Obviously it's gonna require a massive overhaul and a lot of work to accomplish what I see in the video. But that colorful text is definitely ShowSyncHudText.
You can look into setting up a translations file for it ("<pluginname>.phrases.txt") as SourceMod supports Korean for translations, hence the "ko" folder inside "addons/sourcemod/translations" if I remember correctly. The translations file should be fine to put in UTF-8 format allowing the game to read it properly without borking out.
That's the lovely part of SourceMod, the translations. Provided you're using translations it should display the proper localized language for each client as it checks the client's game language and uses that value to determine what language to display. So you could do korean, english, etc. if you really wanted to.
