That's standard percent URL encoding, in this case of UTF-8 encoded text. A URL cannot contain non-ASCII characters (actually, a subset thereof, different subsets for different parts of the URL). You cannot actually have "이윤희" in a URL. To embed arbitrary characters, you can percent encode them. This simply takes a single byte and encodes its hex value as %xx. The UTF-8 byte representation of "이윤희" is EC 9D B4 EC 9C A4 ED 9D AC, which is exactly what you're seeing in the URL.