If you want to use Chinese google fonts, you must check on https://www.google.com/fonts if font support Chinese and if support, then you should set right subset for font. But if google fonts does not support Chinese, then you must upload custom fonts instead.
So if it's system font then what is the problem? You must upload font files in all formats under Theme options > Fonts > Custom section and then set this font under Theme options > Fonts > Family section.
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