MaLer!!! You are the MAN!!
just made another test with .GlobalPreferences.plist, and this time I changed the order of AppleLanguage. replaced en with zh-TW in first place.
Reboot & Boom!! it's there.

so that means we can put other languages into it and without touch original system.
Appreciate for the advice, Maler!!
Pendalf,
Yes, you can also add other languages into and change the language setting.
too bad, I have no idea about programing, can't help with tools.
I will make another try on German to see what will it happen.
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