[tshering]

I am not sure if I understand exactly what you did. If you followed the "method" of the link you referred to, you did two things.
1) you copied the KoboRoot.tgz from the linked page to the .kobo folder of your device.
2) you copie KGothic MB101.ttf from the linked page to the fonts folder in the root of your device.

By step 1 you invalidated the internal fonts Gothic MB101 and the Ryumin font in order to prevent them from interfering.

The question is now, why does the newly installed font not work? By the way, does it appear in the font list? If not, try renaming the font file to Gothic MB101.ttf in order to make the file name correspond to the internal font name. (I am not sure if this really matters, but you can try.)

Unfortunately, you did serveral differnet things at the same time. This makes it difficult to see, what actually the problem is. You say, you also copied Chinese fonts from the Koreader to the fonts folder in the root of the reader. If one of these fonts seems to support the Chinese character range but does not do so, or supports only a small subset, and it happens that the device choses exactly this font for the book titles, this would result in squares or empty spaces. This, by the way, is the reason for invalidating the pre-installed Gothic MB101 and the Ryumin. Therefore, I would suggest, you delete the Koreader-fonts from your fonts folder (in the root) and see whether it helps.

On a site note, by rebooting (powering on and off) you cannot reverse to the old state. You have to restore the original Gothic MB101 and the Ryumin fonts.

Note: I refer here only to the Kobo software. I don't know what is happaning with your Koreader.