Display ko and en subtitles simultaneously in mpv

dualsubs.lua

function dualsubs()
   local i = 0
   local tracks_count = mp.get_property_number("track-list/count")
   while i < tracks_count do
      local track_type = mp.get_property(string.format("track-list/%d/type", i))
      local track_lang = mp.get_property(string.format("track-list/%d/lang", i))
      local track_id = mp.get_property(string.format("track-list/%d/id", i))

      if track_type == "sub" then
         if string.match(track_lang, "en") then
            mp.set_property_number("sid", track_id)
         end
         if string.match(track_lang, "ko") then
            mp.set_property_number("secondary-sid", track_id)
         end
      end
         
      i = i + 1
   end
end

mp.register_event("file-loaded", dualsubs)