The IETF is currently checking the specification of Zstandard compression and the application/zstd Media Type: https://tools.ietf.org/id/draft-kucherawy-dispatch-zstd-01.html
As soon as the MediaType application/zstd is set as standard the Media Type shall be implemented.
Possible mime-detection for tika-mimetypes.xml (second comment has to be changed when the standard is final):
commons-compress version 1.16 and later provide a compressor and decompressor for the algorithm, based on com.github.luben zstd-jni https://github.com/luben/zstd-jni
Attached sampe zstd file (huffman-compressed-larger) and the result after decompressing it.
Decompression was done with commons-compress 1.16.1 and zstd-jni 1.3.3-3