How does php transfer received bytes to Unicode encoding?

How does php convert received bytes to Unicode encoding? in C #, I convert the Unicode encoding of Chinese characters into byte streams and then POST them to the site. However, after receiving these characters, php always displays question marks, how can I transfer received bytes to Unicode encoding ??? How does php transfer received bytes to Unicode encoding?
In C #, I converted the Unicode encoding of Chinese characters into byte streams and then POST them to the site. However, after receiving the code, php always displays question marks. how can I transfer the received bytes to Unicode encoding ??? Php c #
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The displayed encoding is incorrect. you may have used ansi encoding.
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Iconv ('ucs-2', 'utf-8', $ string)