It seems to do more than install fonts that make the characters readable if it can fix alttabbing issues
You're right in what it installs. The possibility I can think of for alt-tabbing out of the game is that they use characters from east asia in the title of the game. When you alt-tab, the little alt-tab prompt (if you hold alt-tab down, you will see what I'm talking about), it can now display the game name properly and allow the switcher to function properly. Not having the East Asia pack probably "broke" the switcher.