Tiny11 was finally released last week, and I'm excited about how clean and smooth it is. But there is a big problem, that is, I am from Taiwan, I use Traditional Chinese, I am unfamiliar with English, I cannot use English OS for a long time, but Tiny11 seems to be unable to add other languages by itself, what should I do? If possible, I would like to add the language directly to the iso, but I don't know if there is a way.
You can't, at least not easily. It would probably be less work to customize an official iso using MSMG Toolkit or NTLite (paid version).
As are many of the "lite" type custom isos floating around the internet in most likelihood; their small size is partly due to removing all of the additional languages, which is why the OP is SOL. Ghost Spectre has the ability to add language packs supposedly, but I wouldn't trust it. OP, if you have low spec hardware, install Windows 10 Enterprise LTSC 1809 (or 21H2). You may think Tiny11 is "clean and smooth" until you need some function that it doesn't have, like IME and additional languages.